I think cost for an elephant mount should be 40pts, it is after all the same as a black coach.
Warmaster ancients has an elephant mount with +2 combat mod for 30 pts, probably too cheap, 50 is better, but in ancients an elephant mount could be said to rampage in the same way as a stand of elephants, including the unit it is with, making it more of a liability, with the rampage rules in fantasy this doesnt work,
maybe use ancients rampage instead?