I was at Cotto Margarito at the Garden a few years ago. Awesome experience if you do it right. That means do your homework beforehand on the undercard fights. Read their backgrounds, know the odds, and put some bets down on every fight. Toss on a nice outfit (jeans, button down, nice sportscoat, nice shoes), get to the arena nice and early. Lot of energy in the arena for these fight nights, it's fun. And this was for two guys that are B level talent towards the end of their careers now.
Vegas fight nights would be even more amazing because you've got the casino waiting for you afterwards.
No chance you're getting into Mayweather Paq fight for less than $1500. There will be no "face value" tickets sold, they all go to promoters and casino VIP's.