From what I've heard, Valve's MVM FAQ is terrible and confusing. You still get item drops every 30min or so by playing MVM as you would by playing payload or any of those other modes. The only thing you get extra for paying is a cosmetic item every mission, and if you complete a tour of duty in Mann Up mode you get a special robot hat or something.
That's pretty much it.
The FAQ is very clear about it. You can play for free, but you won't get hats for winning. You can pay $1, and you can play on a Valve server one time and get a hat.
Or, you can pay $2 and everyone on your team gets a hat. You can stack $2 tickets and essentially get 4-5 hats. Besides, the tickets are tradeable. They'll only cost like 1 refined in a week.