I learned the hard way not to have a rifle re-barreled, just to swap cartridge chamberings. It cost me more than trading and waited about 5 months to get the rifle back with the new barrel. If it hadn't had so much history with me, it wouldn't have gotten done, but NEVER again!
As far as the Rem 742 in 6mm. Buy a box of ammo and save it for hunting. That box should last you ten years if you don't shoot it much.
Then, go buy a nice bolt-action to shoot either in .243 Win or .223 Rem. You'll have more accuracy and it will be much easier to clean.