I can report on several Turnbull jobs they have done for me -- but only part of the info you may need. I have sent them several 1902 & '05 automatics that I have done my own prep and polish work. Typical cost to have lettering replaced and their premium charcoal blue was a tad under $500. Their lettering, logos, etc is impressed into the metal like Colt did it. Others (& I've tried several others) do laser or hi-speed rotary cutting that can look nice but no way authentic. Turnbulls did one New Service blue job, after my prep for approx same cost as others quoted.
While on the subject, Turnbulls did a frame case color on a SAA, didn't require any prep work, charging me $50 for barrel remove/reinstall & $300 for the case color job.
Their in-house labor rates are apparently pretty high as seen from the pricing of their conpletely restored pieces in the $5k range, probably a lot of tedious hand work to achieve 'perfection'.
I once inquired by phone approx cost to 'restore' one of my 1870s SAAs and found the cost started at about $3600 and went up from there depending on new parts needed. My cylinder with all its sharp edges rounded, new $600, tired old wood grips, etc ---- made me give up the idea.