Another vote for REI Outlet. This Jansport looks like a good place to start. Med-large volume (2300cu in), okay back support, 50 bucks.

http://www.rei.com/REI-Outlet/product/767153


Here's a link to the start page:

http://www.rei.com/Search.do?storeId=8001&query=Backpacks&cat=22000016&cm_re=toc*toc*Packs&origin=Outlet_Camp&seq=1&hist=query%2CBackpacks%5Ecat%2C22000016%5Ecm_re%2Ctoc*toc*Packs%5Eorigin%2COutlet_Camp%5Estart