Over the last 15 years, I have rebarreled the Nagant action to 45/70 single shot, 223 single shot, 30-30 single shot, 7.62x54R repeater, 7mmRemMag repeater, and 300 WinMag repeater.
Over the last 52 years, I have sporterized Mausers.
None of this work is cost effective. You have to want to do it for hobby sake.
I got my 1915 Westinghouse / Sako M39 for $90 in 2004. It is just some old military gun, and means nothing as a collector to me.
Right now I am working on a Colt 1849 made in 1859. I am trying to keep it as stock as I can.