It depends on the PPV buys. All the top fighters get paid by the amount of PPV sells. That is why big name like Anderson Silva always wants to pair up with BJ Penn - more PPV buys = more $$.
This is the pay scale (it was revealed during the Randy vs UFC law suit):
-100,000 - 175,000 buys - $1 per buy
-175,000 - 300,000 buys - $1.50 per buy
-300,000 - 330,000 buys - $2 per buy
-330,000 - plus buys - $3 per buy
Brock, Mir, and GSP all made over $4 million at UFC 100. UFC 100 did 1.7 million buys.
UFC 100: Brock vs Mir / GSP vs Alves
UFC 111: GSP vs Hardy did over 750K PPV buys. So this means that GSP gets an extra $2.2 million + his actually salary which is around 400K - 500K.