Jansport makes decent, lower-cost camping backpacks that have served me for hundreds of trail miles. They will blend in (i.e. make you look harmless) better than mil-spec gear, I believe, if that is a concern for you.

Spring is when the new pack lines come out, so last year's models will be dumped on discounters or put on sale soon if they are not already. Look at:

REI-outlet (although they may not carry Jansport, they will have good deals)

Campmor

Sierra Trading Post