Just got the weekly Rock Band newsletter, and select tracks will be discounted up to 50% from 9/21 to 10/4. PS3 Sale only.
http://blog.us.playstation.com/2010/09/17/psn-exclusive-rock-band-dlc-sale-next-week/
R.E.M – Losing My Religion (now $0.99, original price $1.99)
Flyleaf – Again (now...