No idea, my friend Bryan got me my copies for my birthday.

There's the original game for somewhere near $30, Winter Assault expansion for about $20, and the Dark Crusade expansion for about $30 as well. The original game sports the basic 4 Races, Winter Assault gives you 1 additional, and Dark Crusade gives you 2 more to play with for a total of 7 fairly distinct races to play.

I do happen to know that you can acquire it by other means, and it does have a TCP Direct Host/Join option to play with friends, you just can't play on the online service without authentic Keys.