floyd mayweather faces manny pacquiao in las vegas on may 2 .
mega-fight to become highest grossing pay-per-view event in sport .
mayweather 's victory against saul alvarez currently tops the list .
american fighter will pocket upwards of £ 111m if he goes the distance .
pacquiao could earn close to £ 62m if the fight last 12 rounds .
read : sportsmail takes a look inside both boxers ' training spots .
click here for the latest floyd mayweather and manny pacquiao news .