Huntwithme2
It's not that hard for a qualified gunsmith.
In simplest terms unscrew the old barrel, buy a .25 cal barrel barrel of the same diameter as your old barrel. Have the barrel chambered for the 257 Wby and screwed onto your rifle. Have the new barrel drilled and tapped for mounting a scope. Bolt it in your old stock and go shooting.
Not sure if any bolt work would be needed for the new cartridge.
Cost for a barrel will vary considerably, depending if you pick up a used barrel or spring for a top of the line.
Gunsmiths vary by reputation, skills, experience, waiting time for having the work done, and costs. You will need to decide if you will be happy with hunting accuracy or want a true tack-driver.
Im sure you will get some more answers from folks who have had work done or actually do the work themselves. They will have more current costs than I have.
Silvertp