Scorch is a gunsmith, he gave a pretty good breakdown of the cost using a new barrel. Most commercial .25-06 rifles use a 22-24" barrel, which is a little short for the .257 Bee to produce the high velocities it is famous for and why it was around $700. Plus a gunsmith may not want to do that kind of work since it is more involved than simply cuttting a new chamber.
Here is a pretty good basement price for the work being done taken from this website
. Most the local gunsmiths are more expensive than I quoted for the same work.
Rechamber customer's barreled action to a different cartridge-must be same bore diameter. Price:$100.00 and up
Open magazine&bottom of*action for Mag calibers $70+up
Open bolt face for Mag calibers $30+up (time req'd)
Shop Rate per hour for all work not priced $40.00
So you're already in for a minimum of $200 if everything is the minimum price. However you now have to reblue the action after you take a mill and files to it open it up. So now you have added another $100 to the price. So now you will have spent a minimum of $300 and you could probably sell the rifle for at least that as a .25-06, go buy the Vanguard in .257 for around $200 more. So you'll have saved $100 to buy ammunition or reloading components vs. the conversion of the old rifle.
In the end it is the OP's rifle and he'll have to decide what he is willing to spend to get the rifle he wants.