Those two calibers have different bolt faces, thus requiring 2 different actions, or donor rifles.

Do you already have an existing rifle you want to re-barrel, or are you planning on buying a donor…THEN re-barreling?

Where are you at, and are you also aware of shipping costs both ways?

Cut, chamber, crown is about $250.

Yea like Yukonal said, what are you starting with? It's often cheaper to find a donor gun in the same caliber class (I mean bolt face size) than machine your smaller boltface to fit with all the replaced extractors and whatnot.

I've heard really good things about the CTR in .260 Rem which is really close to a Creedmoor. Don't know if the factory barrels are enough for what you're looking to do, but anything with the same bolt face as a .30-06 should work, since that's what most of the cases were developed from.

Tikka likes simple. Just on the available models of this years Hunter there are 7 cartridges that use the same bolt face. Which probably means the same bolt. IIRC Tikka just puts a shorter bolt stop in for the shorter models.

It's probably just going to be easier to just get a good heavy contour barrel from a reputable manufacturer new and fit it to your existing T3 action than to try and find a used one and then have it bored out.

I haven't heard of anyone cutting new rifling into an existing barrel for a larger caliber. Cost would probably be more or less the same as cutting rifling into a new barrel.