The cost of having a custom barrel installed depends on the action, the quality of the blank, and the quality of the install. One thing in your favor is that stainless does not need a blue job - that is getting pretty high for a decent job. You can get a cheap blank from a mass market barrel firm, or a custom barrel from the likes of Hart or Shilen. The install can be little more than threading, chambering and screwing the new barel on, to a full squaring of the action, bedding, custom minimum chamber, etc. I do not have current cost figures for you, but you need to know what you want first.
While I have several full-custom barreled actions with $350 barrels and $400 installs, for a rough-and-tumble hunting .35 Whelen I believe that a lower quality blank and a standard install would suffice....unless you wanted 'special' accuracy.
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