About $30-35 each way. It's likely to be a little more going out than coming back, since Animal Kingdom->Universal is slightly longer trip, but vagaries of traffic and stoplights could make one or the other more expensive.
If you like
FLTours, and don't mind reserving your trip, and they quote you a price that's in the same ballpark, then no reason to not use them. See if they'll give you a price break for using them for both trips.
Don