I personally figure out when my local Blockbuster Video Rental store is getting a new shipment in, and since they take all the discs out and put them in special "Blockbuster" cases...they throw the original, BRAND NEW cases away.
You can ask the management for them and many times they will oblige, as it is garbage to them anyways....or if you need to be sneaky, I suppose one could go dumpster diving...although that is morally questionable (It probably wouldnt be too gross though...how much nasty garbage could a vidoe rental place generate...right?)
As Far as printing covers go....you really dont need photopaper or fancy printers per se....I actually go to my school and print them off with a color laser printer on normal document paper, then use a paper cutter and cut them out nice and neat. It works beautifully. THe only bad thing is that my college charges like 15 cents per page. Still...when you think of it like that...a dollar or two could get you a TON of covers.