Cakewalk sonar from Bandlab is free (as far as I know - it was a while ago). I’ve been running Sonar for over a decade. It works, my friends use it and we exchange files all the time. There may be better options, but this is all I’ve used. My friends with money have taken my tracks into a “real studio” where they loaded them into pro-tools for final mixing (for my material I do it all at home) . If you’re just laying down a bass track, you can pretty much just play to whatever mix they send you (don’t play to an mp3) , export a high quality wave file (every daw can import these) and you’re done.