For the project of spiffing up my lesser '06 AE 7.65, I bought the 6" barrel for it from another (very appreciated) forum member for a C-note. Its chamber end was appropriate to the pistol's new model, short frame, and was an unmarked P.08 style taper/configuration, made in the 70s(?). I had it modified by a local machinist, finished it up myself, then let G.T. use it to "cut his teeth on"
--one of the first few, in the days before head-space gauges in .30 Luger were part of his tooling. Clocking and head-space worked out just fine, so no chamber or other work to do, and when the upper returned from Az., the pistol was assembled into what is now my favorite shooter, which functions and feels great!
Anyway, it can be done, theoretically, for around $200. As I see it, the variables include the initial price of the barrel, whether you have the old barrel to offset cost by trading it in, old barrel already removed or needing removal, and some luck, though in many cases not so much. In addition, if building or working on a shooter, it's all in the LOVE, anyway--well, I might stop short if confronted by the specteres of starvation or homelessness.... And you're going to wind up with a really cool pistol!