Expensive!
New barrel in .35 Whelen (at least $200 for a quality barrel).
Blue the barrel if it doesn't come blued (approx. $60).
Gunsmith charge to install the new barrel ($120 to $180).
Install iron sights on the new barrel (if you like having iron sights) ($40 to $60). Hope the gunsmith has a long jig extension for drilling the holes in your barrel. Lots of them just "eye-ball" it, and I have seen some front sights that are badly canted one way or another.
Then, hope you don't have any follow up problems from the installation, like a tight chamber, or feeding problems, or a host of other things that happen whenever you rebarrel.
You are much much better off finding a used .35 Whelen in very good condition at a gunshow and buying it. This will save you lots of time, money and headache. If you find one, then the seller will probably accept your .30-06 in trade, and you may only be out another $100 to $150 or so.
Most gunsmiths will give you this same advice.
If you spend all of the money to rebarrel, then counting the original cost of your rifle, you will probably have $750 to $800 invested in the rifle, . . . .and you won't be able to sell it for $300.