Around here you are going to pay in between $350-$575 for a full shoulder WT mount.
You want to make sure you get a good tan on your hide and not a taxidermist that still uses DP (dry preserve) Dry preservative is alot more prone to crack and split then a tanned hide. Just remember Eyes, Ears, Nose is what makes a quality mount. Sadly, most people do not have a clue what goes into a quality mount, and get taken for real cheap shoddy work.
Best you can do is ask around and make sure they use the right method, any quality taxidermist studies whitetail reference photos and will get there mounts looking identical to them as possible.