I knew 2 former UFC fighters (circa 2010/2016) that got USD 20K in average for their fights. The issue is that this does not cover 100% of the whole preparation that they need to be in the octagon. For instance, from little things since food and flight tickets, going to special medication (one of them was suspended by the USDA and got banned from UFC), sparring, fighting camping, and so on. One of them told me that the UFC was only the marketing for his personal Jiu Jitsu academy as a top of the pipeline for new students.