here are a few sites i've came across where you can find high quality tracks for your demos and albums. You will be surprised, these sites have a lot of good tracks arranging from $10-$30. Some even have free beats. You may have to do a little searching, but they are there.

www.givemebeats.com

www.igotdembeatz.com

www.mybeatshop.com

www.rocbattle.com