get me into panniers that can double as a backpack.

cos carrying books in a mess sucks and riding with my backpack also sucks.

http://www.ortliebusa.com/CartGenie/prod-209.htm

http://www.arkel-od.com/us/all-categories/urban-commuting.html

the shop my dad works at can get these, so cheap.

Um. Did you just answer your own question?

those look nerdy and complex but cheap is cheap.

no, well sorta. the arkel ones are what my dad said the shop carried. there’s got to be more out there. also might check to see if i can retrofit a backpack to mount to panniers

you mean to mount to a rack?

anyway, what i did for a while was stuff a baileyworks mess bag (mostly full, except for books and laptop) into a pannier. when locking up at school, pull out the mess bag, strap the empty pannier to one of the compression straps, voila.

not ideal, but it worked.

i also picked up a cheap old hiking daypack meaning to do this, then never got around to it

http://www.wiggle.co.uk/p/cycle/7/Ortlieb_Carrying_System_For_Panniers/5360007525/

Ortlieb pannier plug + carrying system?