[Despite]

Official fighter pay is reported to state commissions and can be found on many sites after the event. What is not disclosed, and is probably the lion's share of most fighter's income, is sponsorships.

I don't know who gets a cut of the PPV -- I suspect GSP and Silva and not many others. For the rest, their disclosed pay is in usually in the low 6-figures.

In the past there were a ton of stories about tactics used by Dana and the Fertitta's to keep overall fighter pay down. E.g. they wouldn't bring in fighters who were making big money at other promotions (such as Fedor and Overeem), for fear of setting precedents. They do seem more open to that now, though, as Overeem is in the UFC and Fedor might be soon.

Edit: Some examples from the last event (copied from Wikipedia):

Henderson - 250,000

Rua - 165,000

Wanderlei Silva - 200,000

Cung Le - 350,000 (total WTF)

Faber - 64,000 (including win bonus, plus Faber is a huge draw, another WTF)

Bowles - 19,000

[Maven911]

And you have to remember that they rake in millions in ticket sales and more importantly pay per view deals, yet they keep salaries naturally depressed for people who are risking serious short-term and long-term injuries. There is good reason why all major sports have a players association to negotiate he collective bargaining agreements with the owners