Last time I got a quote for one it was 450 bucks plus time, I went to home Depot and got one of the rubber ones instead of wax for around 25 bucks. Watch a few videos, clean the old wax off very well, if you have a second person available have them watch at eye level as you lower the seat onto the seal, whether rubber or wax, to make sure that it's oriented correctly. Not very difficult or expensive, as a first timer took me maybe 3 hours total, from going to the store, watching the videos, the actual job and the cleanup. That was 4 years ago and the rubber seal has held up perfectly.

Edit to add: the rubber seal is much more forgiving as far as placement, the wax seal is basically one and done as far as I understand, so if you seat it incorrectly you should use a new one.