It is free to play though you can pay to accelerate your progress.
Check out the youtube vids, it is GORGEOUS for a free game. They had gotten funding from about $1.5mil in donations, aye, the fan base is still going strong! My ONLY two complaints that I've seen so far without having played it is that it uses CryEngine 3, which I wished they could have worked something out to get the Frostbite engine as even the trees don't go down when they're run through. The other thing is that the mechs don't go critical if they recieve enough damage, that really kinda bothers me. BUT a cool factor is that the game is set in a 1:1 progression rate for the actual timeline. 2013=3050, which means by the time they come out with some downloadable content it will be related to the Clan invations.