Shogi,
This is normally done while rebarrelling, so improvements could be attributed to more than one variable. You are looking at about 4 hours labour to square off a Remington action and bolt-face, re-cut lug recesses and rethread the action. In addition setting back the barrel one thread and rechambering will go for $200-250. This isn't the way things are usually done though.
I got a factory barrel on a XR-100 rechambered to 22/243 , strictly as a throw-away fire-forming barrel and the action prepped at the same time as well as fitting a Lilja barrel. The damn thing shot so well like that, that the throw-away barrel is still on the gun and the Lilja is still waiting. 5 in one hole is too good to take apart so the fitted and chambered Lilja is still gathering dust. Ironic, isn't it?