Turnbull has a $100 minimum on C/Color work now AFAIK.
Call and maybe you can get X number of locks done for that,,,and maybe not!
He used to charge $50 apiece for S&W hammers and/or triggers for restorations I did.
Heintzleman's uses Cyanide case coloring. I don't know if they do bone/charcoal c/coloring too.
We used them for recoloring AH Fox shotguns in the same cyanide colors that Fox started using on their guns after WW1.
Heintzelman was in fact the same company Fox originally use back in the 20's and 30's for their cyanide case colors.
Last one (Fox) I had done by them was about $100 for a complete action w/forend, lever, ect. But that was perhaps 12yrs ago.
Classic Guns/John Gillette doesn't list anything for small parts case coloring. Gotta call I guess.
He and Turnbull and some others like Rons Gun Shop used to charge $50 each for things like hammers, trigger guards, etc.
That was a couple of years ago.
http://www.classicgunsinc.com/pricing.htmhttp://www.ronsgunshop.com/pricing.htmlSeems to be alot of smaller lesser knowns doing CCH now. Some doing work just as nice as the big names. Best bet would probably be to seeek them out and get their pricing in hopes of a better break.
It takes the same time to do the process wether it's a big/small box,,full or not. So to make a run costs the same pretty much for the purveyor of the art.
I've seen some great work posted here of late.