Depends on who's fighting. If its someone like Anderson Silva, he'll haul in around $200,000 a fight. Your average fighter will haul in around $90,000 a year. Prelim fighters will haul in less than $10,000 a year.
Just depends on the kind of fan base a particular fighter can haul in. Thats why fighters will typically trash talk, make up fake drama, to bring in more fans.