Glad you've enjoyed our game! Yeah, this volume raymarching stuff was quite a mountain to climb... A mountain with a ton of graphical artifacts along the way. As for the music, there is nothing really to pay for, I just took a guitar and a harmonica and did an improv for a couple of minutes. There is even an incomming Discord message sound right in the middle of the track that we didn't bother to remove!
Anyways, I've posted a link for an OST download down in the comments on the game's page.