I just had an interesting idea- what if there was a site like eBay for downloadable music. I mean, a place where anyone could set up an account and post a piece of music so that people could buy it. The composer could set his/her own price. Maybe the site would collect a 10% commision or something. Maybe it could work...

Try Sibelius Music...you can post a piece for people to view/buy.  I've never done it myself, but I have browsed around. 

http://www.sibeliusmusic.com/

Thats cool. I didn't realize anyone had tried this yet.

Finale also has something like this on [url=http://www.finalemusic.com/showcase]www.finalemusic.com/showcase[/url] but it is geared more towards free sharing of music.