Perhaps the upkeep could be increased via a factor of two instead of just being a simple addition per level, so lvl 1 would have an upkeep of 3, lvl 2 an upkeep of 6 and lvl 3 an upkeep of 12

I like that idea! This way we don't overcomplicate things and still offer some interesting strategic choices. "Do I want to sacrifice a more building slots or upgrade the ones I have with the downside of paying more upkeep?"

I second @.Del's idea.

I like Del's idea. I think the keepup is better to triple from lvl 1 to 2 (because job increase from 1 to 3), and double from lvl 2 to 3 (because job increase from 3 to 6). Or just simply triple the keepup for each upgrade.

I don't necessarily agree. While it could be good for a general cost balancing, I think it would be good to first set a goal: Do we want only a general balance for costs, do we want to keep somewhat do the base games upgrade themes, do we care about the fact, that minerals are now(since the new economy) more scarce compared to energy, and how much we want to upset base game balance.

A further thematic problem is that ingame-wise we are talking about a technological difference, which, I think, should somewhat reflect in shifted raw resource costs, which is somewhat in the base game. For latecomers, I have some calculations in the comments, which I think reflect this. Other things to consider could be the fact, that in vanilla refineries are a sort of filler building, with vastly lower job count that is needed to open the next open slot, making building dedicated refinery worlds quite hard to build.
The current 1/3/6 jobs modell of the mod first eases, then completely legitimizes the making of these worlds. furthermore it completley blows out any other building upgrade line by multipliying the base job number at maximum level not just by the usual 4, the highest 5 of the unity chain, but by a whooping 6. That is a lot of free building slots, which, I would argue, are currently one of the most valuable resources in the game. In their current form I think the current 0/1/2 SR upkeep is absolutely needed, if not straight up low, and I don't think merely 3 or 6 extra energy cost on the building would be enough.

On the topic of @.Del's concern regarding circular upgrading(again, this conversation's precursor in the comments. I leave it to your discretion whether it can be found with 6 anomalies or a series of archeological sites) while with wrong numbers it definitly could be a problem, I don't think the current numbers would actually present any problems, given that a fully upgraded refinery requeries a base of 2 SR monthly while fully manned produces a base of 12, which is still a net gain of 10 and a pure gain of 10 of each with 1 fully upgraded refinery of each type. Furthermore, since you need these to upgrade multiple buildings, you usually want to have some spare production and not use every single unit of them, not to mention fraction units which come from upkeep reductions and production increases. This makes me think this would be easier to manage than it seems at first sight.

Now onto my ideas. I would actually introduce an extra tier for the refineries and techs balanced somewhere around 1/2/4/6 jobs in the manner of the unity building chain. This could delay both the need of other SR as upkeep to 0/0/1/2 and the advent of absolutely broken refinery worlds(I can already imagine making full use of that -25% job upkeep modifier with these).

Oh and @Jurjen , I'm the complete opposite of that, making quite good, or at least decent guesses at balance and trying to look for the limits of the code and orthodox and unorthotox solutions, but I can't make even a half decent sprite for the life of me... Oh, and I won't approach within 5 meters of Stellaris AI :D, khrm, khm, so if you would like, I would be happy to work with you on a few projects.

Alternativley we could skyrocket the building upkeep and give the higher levels a few custom jobs, which would "recycle" the upkeep to usable raw resources, effectively reducing it. This could circumvent the SR cost and introduce a need for low(er) raw resource->SR or lower workforce efficiency. I have a few other ideas, but those involve tinkering with vanilla jobs, which is generally a bad idea for compatibility, so I won't list them.

PS.: aaand I again wrote a wall of text... Sorry everyone, this seems to be a wordy day for me.

i say just up the energy cost, Like what Del said

If I may jump into this discussion, the only reason I can see for having the upgrades cost other SRs is when we want more of one SR and less of another. But then, we'd just build more of that refinery and less of another. Another layer of complexity that boils into a best-use-case of a set of all 3 + 1 of the one we actually want.

On a related note, iirc, SR upkeep is for the building, not the jobs, so any job upkeep modifiers only apply to Minerals while building upkeep modifiers affect both Energy and SR upkeep.

I understand upkeep of Zro/LivingMetal/DarkMatter/Nanites would be silly.

I'd say just KISS it: the buildings give 1/2/3 jobs with 3/7/11 Energy upkeep. No SR upkeep.
At 3 jobs, the building plus just one district of any kind is enough jobs to open a new building slot.

Edit: I like the sprites, btw

If there really is a need for a secondary upkeep, perhaps use research points as upkeep? One of the admin cap tech mod allows you to build buildings to give you more admin cap but at the cost of society research points. Perhaps something like that can be used as well?

Volatile Mote- Engineering Research (Due to motes being used in explosive and kinetic weapons, an engineering tech)

Exotic Gas- Society Research (Terraforming uses gas to terraform faster, a society tech)

Rare Crystal- Physics Research (Due to higher grade laser weapons using crystals, a physics tech)

Make it so that only the second and third stage S.R factories requires them as upkeep, perhaps 10/20? The numbers can be changed but basically if you have alot of those, it'll eat into your research due to a lore reasoning that the higher tier buildings need scientists who knows what to do to supervise the factory so it doesn't blow up or anything, thus taking them away from researching new tech for you.

Yea, Del's ideas seem pretty good in both balance and gameplay. The SR upkeep seems okay, but then you just build all 3 plus extras as steelcrow already pointed out. Research is something we have plenty of late game, and if you start using tons of these refineries it could cut into your research. Granted, energy is the basic cop-out resource for upkeep, and see no reason it wouldn't work. If Your worried about what everyone wants, maybe make 2 (or more) seperate versions of the mod for those who want different balancing. My personal vote is for either the research or energy upkeep.

While research seems good at first blink, don't forget that if you are at a point where you need these buildings, you probably use upgraded labs anyway which effectively means an overuse of exotic gases, and consequently, society research.
If the mod's is to move into this direction, I would rather propose a mineral upkeep for the buildings instead of the SR, rather than overinflating energy upkeep. This would make it simpler, while keeping a higher mineral cost, which makes it harder to spam it with ringworlds/habitats.

That being said, I'm not one to argue against literally every other speaker's opinion in this regard(unless I'm in a Reaally good mood), nor am I the developer, furthermore I feel like I contributed my 2 cents to this discussion, and also conveyed my general ideas about balancing, so I will generally try to refrain from further comments, unless asked...(if you, dear reader, wonder why I shared this part, this is also a reminder for meself, I tend to be forgetful in this regard).

The Galactic Community has spoken! Thank you all for sharing your insights. I'm glad I asked because not only will the mod progress now, I also have some great inspiration for the future. I will now pull my head out of the Matter Decompressor and get to work.

I have decided that for now I will go for an overall increase of the energy upkeep (3/6/12) and refrain from adding strategic resources or research as secondary requirements. This is the most conservative solution, but I'm confident it will work better than anything I tried before.

Honestly it is op. Because more advanced buildings dont introduce more upkeep per strategic resource produced. IMO, upkeep should be MUCH higher. You cant create more jobs per slot without serious upkeep in this game. I think that more advanced buildings should have 2\3\4 specialists (because 5 does open another slot and this is a serious balance thing) and they should have much higher energy AND mineral upkeep. Keep the basic jobs, but add mineral upkeep to builings, it is very easy compared to writing new jobs.

I'm up for increasing the upkeep. But I'm less happy about reducing the amount of jobs. Not before the game gives us better ways to handle mass unemployment after you run out of districts and building slots.

Upgraded commercial zone gives around 11 jobs\slot, if I am right.
Well, its not a question of jobs provided, it is more of a question about upkeep and overall balance. Basic building gives one job per slot and it is VERY hard on planet infrastructure, because you need 4 jobs in some other area to open another building slot. Which probably means upgrading some building to have a strategic resource upkeep, which lowers overall efficiency of a refiner. Therefore, the upkeep for basic refineries is quite modest, because of these 2 things. However, when we have like, 4 jobs, we need only 1 job to open another slot, which isnt the same as having to make 4 jobs. For example, an upgraded commerical zone (which probably gives the most jobs) gives 11 jobs and it can compensate for either 3 vanilla refinery or basically, 10 second tier refineries from this mod. Which means you waste each 4th slot on commercial in vanilla or 1 in 10 slots on tier 2 refinery from this mod to open new slots. Therefore, in my opinion, this can only be legit if these refineries have their upkeep pushed to some ridiculous-to-♥♥♥♥♥♥♥♥ level. Otherwise it is quite easily exploited in both slots and trade. Its definetely legit and fair if tier-3 costs something like 100 minerals + 5 jobs upkeep to get 10 strategic resource where each sells for around 10 energy and opens you another building slot.

However, I think 4 jobs at tier-3 is a sweetspot, because at this point you dont need to push the upkeep as hard as 5 jobs per slot. Each job gives 2 resource, so its a big deal what is resource per slot you have, 8 per slot or 10 per slot is definetely a huge deal. Vanilla gives you 2 per slot, just to remind.