on average I would guess any where from 300 to 500 bucks is the norm, range IMO!
a lot depends on the person doing the work, there skill level and well, what they charge
NOT all taxidermists are up to the same skill set, I highly recommend you learn some things to look for on mounts, to tell GOOD from bad one's and then go visit some taxidermist near you and see what there work looks like!
a good taxidermist that is ALWAYS consistent, is rather hard ti find IMO
and some time,s price has NOTHING to do with quality either!
also ask for turn around times, and if you drop anything off, get something in writing with prices and estimated return time!