Tell us more about the specifics of the rifle you are considering.
Musgraves are lovely actions; my principal target rifle is one, and I just love it.
Like other user target rifles, especially older actions (Sportco, Swing, Musgrave), they really don't fetch a lot of money on the market. That's great if you're buying, not so good if you're selling.
As a buyer, you have to assume that the barrel is shot out or nearly so; even if it is match grade barrel, properly chambered, it doesn't make sense to pay any more than $200 for the barrel portion of the rifle (and that's assuming it's shooting well). Remember a brand new match barrel, of your choice, installed as you want it, is no more than $700-ish. And it *really* has no rounds through it.
For the action portion, there's no way I'd pay more than $1000 (since one can get a modern, new action such as a Barnard for not a whole heck of a lot more than that). For a Sportco I'd pay $300-$500 for the action, for a Swing perhaps $700 or a bit more (they're good actions but they are a pain in the ass to use and they do break parts from time to time). For a Musgrave in rough shape but perfectly usable I would pay $500-$600 and not feel like I was ripping off the seller. A Musgrave in very nice condition I'd go closer to $1000.
For the stock, even if it cost $1200 to buy and build, it'd have to be a pretty nice stock to add more than $500 to the value of the gun.
Does it come with rear bases or front bases for iron sights? What about scope mounts?