Music is all finished for the demo, but I haven't posted anything about it. I thought I would do so now. Since I'm not the most capable composer, and I don't have a lot of money to contract it out, I've been using public domain sheet music. There are multiple sites with large archives of it, dating back to the 14th century and beyond. And, AFAICT, music notation hasn't changed much since then. I was using the International Music Score Library Project before it recently got shut down. Now I'm using the Werner Icking Music Archive.

My workflow goes as follows. Browse the site until I find a piece that would be appropriate for the required atmosphere. Fire up Rosegarden and enter the music by hand. Select the instruments according to my General MIDI instrument range guide, which is probably of questionable technical accuracy. Play with the levels and export to MIDI. Use Timidity with Frank Wen's Fluid R3 soundfont to render to WAV. Compress with FLAC and Ogg Vorbis.

Of course, custom music by an indie with good synths would be preferable, but this solution provides reasonable quality without any expense.