That's great, thank you so much CRS. There is a great community here.

Been a while since I made this, but IIRC it worked like this:
1. Find SE's files that define contract rewards and listing fees (namely, ContractTypes_Economy.sbc and SessionComponents_Economy.sbc)
2. Create a folder for your mod and copy those files in there.
3. Tweak the values in the .sbc files to your liking.

You could also take a look at my files directly if you want to reverse-engineer what I did.
If I'm not mistaken, you should find the files in your Steam directory under "steamapps\workshop\content\244850\2451205497".

May I ask you how you did this?