Note: I am not knowledgeable about audio compression or audiophile stuff, but with the power of the Internet I believe I can explain these concepts well enough.

There are two types of data compression: lossy and lossless.

• Lossy is data compression where some of the original data is thrown away.
  
• Lossless is data compression where none of the original data is thrown away. Using some very clever techniques, lossless compression methods find redundant data and store it in a more efficient way than it was before.

BallisticNG's soundtrack is released on the Steam Store with all of its files only at MP3 320kbps, a lossy format.

For obvious reasons, lossy data is not good for archival purposes, since some of the original data is lost.
Many also claim to be able to hear a difference between a lossy audio stream and a lossless one. For the average consumer, this doesn't really matter and you probably won't be able to hear it. You need to have good equipment as well as a trained ear.
But people care regardless, like myself. I enjoy owning my music in lossless quality because I know I have the most high quality version of the track. Combine FOMO and human's innate desire to collect things, and boom: you now care about owning your music in the highest quality you can obtain.

This guide is made based off of the track listing on September 18, 2024. An archival capture of the page as it existed then is available here.[web.archive.org]

Template: (PRICE) ARTIST's TRACK_NAME/ALBUM_NAME: NOTES

(0) Vonsnake's Taurus[vonsnake.bandcamp.com]: The game has the BNG Edit version, which is different from this longer version.
($4) Shiftdelete's BallisticNG Sessions album[shiftdelete.bandcamp.com]: Contains additional remixes not present in the official soundtrack release
(0) Shiftdelete's Moln[shiftdelete.bandcamp.com]
(0) Shiftdelete's Skyline[shiftdelete.bandcamp.com]
(0) Shiftdelete's To The Finish[shiftdelete.bandcamp.com]
($1) Shiftdelete's Shockwave[shiftdelete.bandcamp.com]
($4.45) Shiryu's Flinch Twich[shiryu.bandcamp.com]
($1.32) Paradise Decay's Blade II Project[paradisedecay.bandcamp.com]: According to Lt Phoenix's OST review, this and the following track are named differently on Bandcamp and on BNG's OST, but they are in fact the same track.
($1.32) Paradise Decay's Island Sun[paradisedecay.bandcamp.com]
($1) Atlanticore's Slipstream[atlanticore.bandcamp.com]

• All of Vonsnake's material minus Taurus
  
• All of Xpand's material
  
• Shem - In Saturns Rings (BallisticNG Edit)
  
• Shem - No Gratitude (BallisticNG Mix)

Vonsnake specifically exported all his work in MP3 format and reportedly deliberately worked with lossy samples. Lossless versions will never be released/don't exist; the lossy quality is his artistic intent. The highest quality you can get is the official version on the Steam page.
Kabelsalat and Rad are both moderators of the BallisticNG Discord; this is a screenshot from that Discord. You can probably find a quote directly from Vonsnake saying this but I'm too lazy.
Xpand's Bandcamp is here[xpandrbng.bandcamp.com], but none of its BallisticNG content is available. It switched aliases to -kx, and then to psiX. It now goes by neuralfold[neuralfold.bandcamp.com]. It's in the Discord still, and quite active, so I've messaged it asking if the lossy format is part of its artistic intent. Will update when I have an answer.
Shem appears to have purposefully deleted all their music and socials and disconnected from the internet. Here is the last available archive of their Bandcamp[web.archive.org].
Vonsnake himself says[discord.com] "...not every song was sent lossless and Shem seams to have disappeared off the face of the planet so I can't get those...".
Note: The URL linked above goes to a Discord message in the BallisticNG Discord.
Bonus: An extended version of In Saturn's Rings is available on YouTube here.

PS: There are also songs that were at one point with the soundtrack of the game but got removed for various reasons. You can view the Wayback Machine's archive of the soundtrack page[web.archive.org] yourself and check.

So to obtain all of the songs at the highest available quality, you need to:

• ($6.99) Buy the Official Soundtrack
  
• ($4.00) Buy Shiftdelete's BNG Album
  
• ($1.00) Buy Shiftdelete's Shockwave
  
• ($4.45) Buy Shiryu's Flinch Twich
  
• ($1.32) Buy Paradise Decay's Blade II Project
  
• ($1.32) Buy Paradise Decay's Island Sun
  
• ($1.00) Buy Atlanticore's Slipstream

Your total is $20.08 before taxes.
If you already have the OST, you have to pay $13.09 before taxes to get the available songs in lossless quality.

Thanks to BallisticNG for a great game, and all the artists mentioned above for a sick soundtrack.
Thanks to Lt Phoenix's review for helping me find a couple of tracks and piece together some stuff.