You can pretty much guarantee WM would get 800,000 buys (Only XIX at 640,000 and 14 at 730,000 were less in the last 10 years).
So at $55 a PPV (not counting for HDs $15 more) they'll have to break last years record of 1.188 million buys to recoup the cost of Mayweather.
I dont think that will happen even though the card is looking more solid than last year.