Pick up a used 1B barrel in a smaller caliber and have it rechambered and bored to whatever you want. You may have to go to another nonmag extractor if you leave the mag calibers out. Should cost less than $300 and the half dozen I have had done over the years have shot better than Ruger factory barrels. Those I have left include a 338 Federal, a 338-06, a 6'5 Swede, a 7mm-08, and a 9.3x62.
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The seller could/should? take less than $500 if you deal hard nosed on it. The value of a barreled action is @ the price suggested and that barrel is toast. It probably will need a reblue in the bargain.
Good luck,
wunbe