I just came across this. Offered by Song Galaxy, it's called Multi Tracks. It allows you to download songs that are in audio format,but in separate tracks. You can then edit and/or remove tracks and then save the end product as a .wav or mp3 file. There's a free software that can be tried with one of their demos. Check it out at:
http://www.songgalaxy.com/pages.php?content=multi_tracks

£10 per song... (@ $15)

Kind of pricey to put together a few hundred song repertoire, IMO...