well , I used to have a very close friend that used to mount all mine, well he did about 25 fotr me!
and did it at just costs for me, and that was under a 100 bucks a head for yrs , yes I was spoiled for sure!
and he did great work
BUT he stopped doing it a couple yrs back, and I have been looking for a good replacement, and not having any luck really either!

the last 4 I had done cost me between 300 and 450 bucks, and to be honest, I wouldn't go back to them again,
as the heads came out, not so great
I think most taxidermist kinda count on folks not knowing the difference between a GOOD mount and a SO SO one!, and sadly most guys don't!
always said most guys find out a head is bad after they get one back that is good and put it next to the first one!

as for how long it takes
I have had heads done in under 3 months

MOST , NOT ALL< shops wait till they a bunch of hides to send in all at once, get a better rate on tanning than(well those that don't tan there own ), and MORE profit for them then doing so,
and why it takes so many so long, as if they send them out all at once they get them all back at once, so if they send out 50, they get 50 back at same time, thus a LOT of work to get them all done
and personally, I think thats also why some turn out a few great heads, then as they get tired of working on abunch at a time ,
say burned out
and then try going faster and quality slips, meaning you might get a great mount and guy behind you gets a SO SO one, or worse
its not the guy doesn't have the skills, just they don't put 100% in all them when they start to get behind or, just tired of working on them!

I have also seen this with many taxidermist ordering a certian size form, like a one size fits most then!!
they take an average size form and order a BUNCH of them to get a deal on them, and then some guys get a form, a lot smaller than the deer they killed, and don't be happy with what they get back

AGAIN, NOT all do this, but sadly a lot do in my area any how
a good taxidermist is not easy to find if you ask me, and a dying art almost!!
sorry if I got off topic, just giving some info I happen to know about on this