I'd rate the prices rather high unless modern movements are trickier than old Valjouxs. My 1960's Heuers with Valjoux 92 or 7730/3 come out at a bit over 200 quid, plus whatever parts are need -- normaly just a mainspring.
At >10 years old I'd get them checked, but after discussing with my usual watchmaker he recommends keeping an eye on power reserve as well as time drift. When either starts to change significantly that's the time for a service. As I am looking at a computer screen for several hours a day it's easy to note these things in a spreadsheet every few months.
I use Rich Askham in Yorkshire for Heuers and related makes, but as he will not do Omegas I have to look elsewhere. Simon Freese in Essex is highly recommended for Omegas but I haven't sent a watch to him yet. There is also Chris Nicholas in Somerset and Nic Green within earshot of the M25. Have not dealt with either but they have very good reputations in vintage circles.