I'm not reading an apples to apples comparison here:
Buying a brand new pair of underwear has a very different implication compared to buying a "slightly used" pair of underwear at the same price.
Applying a certain dollar amount for a used rifle - as you mentioned, with unknown barrel life remaining - is not the same value as the same dollar amount applied to a brand new barrel, even if it was just an unfired take-off factory barrel, let along comparing against a custom tube.
I'd rebarrel. It sounds like you'll be break-even on cost if you don't sell your rifle, or you'd be break-even on legwork to compare selling your current rifle against finding a barrel and a smith. But getting a known quantity brand new barrel is a better value than getting an unknown quantity in the used rifle.