The purse is calculated as such:
((Average value of all non-infantry units) / 2) * (Arena Modifier) = Monies!
Arena Modifier: Off-Circuit = 1 Minor = 1.5 Major = 2
Winner recieves 100% of purse value minus 2nd and 3rd place.
Runner up recieves 20% of purse value.
Next in line recieves 10% of purse value.
Anyone after this recieve nothing but the shame of their horrific loss.