As far as I know Nate at JNC MFG is the cheapest and best I have ever used.
M2's and M3's are about the only thing I don't do anymore, he charged me $1000+Shipping back and hard chromes parts.
He may be more now, but I have known him for years.
Ive bought, post sampled, and sold over 30 of his guns.
Had one come back today to convert back to semi, probably the nicest 50's I have ever seen and I know many a people who have had Ramo or crappy Group guns I have sent in to get rebuilt on registered plates as well.