$50 to $75 is the low end with perhaps $125-$150 for the high end for a takeoff barrel if the round count is low.
I have purchased many takeoffs over the decades.
I have a lathe and a dozen reamers with lots of tooling. I do all the work myself. I can try a chambering for very little outlay. Most of those takeoffs, if they have a low round count, shoot quite well.
I have purchased takeoffs in Remington, Winchester, Ruger and most recently a Tikka.
While I have placed a Rem takeoff into another Rem ending up with proper headspace, I usually use the takeoff by rechambering it with a larger reamer which removes the original chamber.
As for receiver threads it depends, I'll use it or make my own. I typically put Rem takeoffs on a Rem receiver. A push feed Post 64 Win or a Ruger M77 are easy to thread as there is no extractor cut and if a Rem takeoff is used the threads for these two are smaller so most of the rem shank can be used to maintain the length.
A few examples: 243 to 6mm-284, 300 Win to 300 RUM, 7-08 in 284 Win and 338 Win mag to 338 RUM. That Tikka was a 25-06 which is now a 257 Weatherby.
I have also cut off a portion of a 308 chamber and barrel shank to make a 30 BR. Same for a shortening a 243 to make a 6 BR
There is a market for lighty used takeoff barrels.