ARMA 2 Question

I there a way I can download Arma 2 CO and buy a cd key and put it in and get the game cheaper

try torrenting the game.

Download DayZ with this video
I did it with the link of nico's blog.

When thing's are working fine and you can play on no cd servers just download the darky cd key changer , buy a legit key and change your previous key with the darky cd key changer.