Here a link to the before and after pictures of some of the restoration work Turnbull's can do. The prices range right on up there to reflect the quality of the work, too. Buying original guns and then sending them for the full treatment certainly makes them grail guns.
Here's the before on a Colt SAA, it had been in a fire.
Here's the after.
There's no need to start with such an extreme example except to show what is possible. Go and look at the work they are doing, on old restorations, as well as their reproductions and modern firearms.
Just the original firearms are spendy, add a full restoration, along with a personal range to enjoy them on, and we have another interesting grail gun choice.