you can get the CD for really cheap anywhere, and sometimes you don't even need the CD. the authentication key, on the other hand, is going to cost you no matter what. try to find sales on canadacomputers, ncix, or amazon.ca from time to time. i've noticed that Win8/8.1 is cheaper than 7.
update:
or if you're really desperate and don't mind tinkering a bit, download 2012R2 Essentials (server) and use it for free. just ignore the pop-up after 180 days. legal. free.