You guys are funny. The average ranked MMA fighter is making more per fight than the average ranked boxer. The only reason this is so high in the pay scale is because it's Mayweather.
The average MMA fighter would also kick the crap out of the average boxer in the octagon.
I think Mayweather will win in a boxing ring...but it would be even more one sided in the Octogan (To McGregor's advantage obviously).