The UFC DOES pay for airfare and hotel for the fighter + 1. However, for fighters from Korea, we have to come in at least 10 days early (2 weeks is better) in order to get used to the time difference. The UFC tickets flights (and books the hotel) for 4 or 5 days before the fight. So, the fighters from Korea (and other foreign countries) have to pay the difference in fares and the extra days for room and board.
If you assume that a fighter is going to bring, at least, their coach and a sparring partner (for KTT, they bring me as well), that means the fighter is paying for 2 extra plane tickets (usually between $1200-2000 RT from Seoul). Add in 5 or 6 days of room and board for 4-5 guys and it starts to add up! Then take out US federal and state taxes, then the guys get taxed again in Korea. Subtract paying the fees to the coach and sparring partner... and what's the fighter left with? Unless they get a bonus (or two), or are making a really good base pay, not much.