http://www.teamfortress.com/mvm/bounty/
Just so we're clear, it's 99 cents for a random chance hat/misc drop. The game mode is pretty much free. You only have to pay for the rewards, which are entirely cosmetic and non-gameplay affecting. So no incoherent nonsensical rage, please.
Edit: Update is out.
Oh yeah, MvM servers are 32 player servers with 6 slots held by players and the rest by bots/spectators.