Credit Dave Meltzer of www.wrestlingobserver.com for the numbers.
The winner is only guaranteed the first year; if they go on a losing streak or are boring and the fans hate them, the UFC can cut them by year two. The pay is on a sliding/increasing scale each year. It is for 3 fights per year for 3 years or 9 fights if the contract is fullfilled.
Year 1: 12k guaranteed/12k win bonus per fight = 72k if they win all 3.
Year 2: 16k guaranteed/16k win bonus per fight = 96k if they win all 3.
Year 3: 22k guaranteed/22k win bonus per fight = 132k if they win all 3.
If a fighter wins every fight, it adds up to 300k total by the end of the 3 year contract period. Thats a tall order to win 9 fights in a row.
TUF losers who are being used are typically offered 3 fight deals at 5k guaranteed/5k win bonus which is also what the finalists are paid (Rashad v Imes). Dana doesn't hire every TUF contestant.
This is backed up by the salary info from the TUF 2 finale show:
Jardine (10k win) over Schall (5k loss)
Guillard (10k win) over Davis (5k loss)
Burkman (10k win) over Morgan (5k loss)
Florian (12k win) over Cope (2k loss)--Dana is using Florian to help evaluate talent for TUF 3 so maybe thats why he gets a bump. Cope really went in the hole on this fight since his elbow and clavicle were injured.
Stevenson (10k win) over Cummo (5k loss)
Evans (10k win) over Imes (5k loss)
Sanchez (24k win) over Diaz (10k loss)--so Diaz was correct that Sanchez gets paid more than him to show; 12k vs 10k.
Considering the training costs, travel expenses and ancilliary money spent to be a fighter, the winners are hardly getting rich. If they can win and make it to year 3 the payoff finally comes. And if they are on a 9 fight/3 year winning streak, the UFC will undoubtedly re-sign them to a bigger deal.