The capacity at the MGM Grand is 16,800. Once you take out the seats for the media, production people and what not, you are left with about 16k seats for the public.
Tickets for Mayweather-Pacquiao are in high demand, but you probably won’t be able to buy one at face value. The reason being, the majority of the tickets aren’t going to be for sale. It appears one of the final hurdles in getting a deal done was the ticket distribution. ESPN breaks down the how that dispute was settled.
Neither side wanted to disclose what the final issues were, although one source with knowledge of the deal said that how to divide the roughly 16,000 tickets was the last sticking point. Ultimately, they settled on a split in which one third of the tickets will be controlled by Mayweather/Showtime, one third by Pacquiao/Top Rank/HBO and one third by the MGM. If there is any public sale of tickets it likely will be very few, perhaps 1,000 just for show.
This is very much like the Super Bowl where face value tickets are very hard to come by. Most Super Bowl tickets go to corporate entities and not at lot available for the public. The difference is most Super Bowls are held in stadiums that seat over 70k, so your chances of finding a reasonable deal on the reseller market is high.
With the MGM only being able to hold 16k you are going to have to pay at least 5x face value (with face value starting at $1k) to get in the building.