Not necessarily true...
Building anything on a surplus action is an economic mistake IF you ever want to recover anything close to what you'll have in it.
That really depends on the quality of the conversion, and who did it.
Tell me the aforementioned Peerless, as well as Sedgely, Griffin & Howe, Surkamer, and P.O. Ackley conversions don't command a premium these days.
Likewise, this isn't exactly true, either:
What you'll end up with is a bunch of money tied up in something that won't shoot as well as an off the rack modern sporter that will be problematic when mounted with a scope (safety will require modification or you'll have to leave it off) etc. and you'll take a huge beating when you sell it.
My Krieger-barreled 98 Mauser conversion below in 6.5-06 will outshoot anything off the rack, save for maybe the high-dollar pieces that can go 1/4 MOA straight from the box. For the money, I did just fine building it and not buying a Sako TRG or Accuracy International. Plus, I have the satisfaction that I built it to my specifications, it puts 10 rounds into 8" at 1000 yards, has cold-bore centerpunched a golf ball at a documented 500 meters, and it will remain a thing of joy for my personal use. Regarding the resale value - pfffttt. It ain't for sale (as a crime novelist wanting a ballistically untraceable rifle and extending several thousand in cash found out), and my coffin will be large enough for the both of us when I take my dirt nap.
Realistically, nobody builds a sporter rifle from a milsurp action these days to save money, get rich selling the finished product, or compete against Wally World. They do so because they want something unique, something that serves a specific purpose, or because the gun is so badly abused it's no longer economically feasible to restore it back to full military condition. That 1916 Haenel action above was an example of a Gewehr98 that was so badly butchered by Bubba with a hacksaw that it became the basis for my 1000+ yard precision rifle. So don't arbitrarily poo-poo somebody's desire to build a quality rifle from a milsurp action. Or am I just insane to hang a Krieger barrel, Canjar trigger, and Vais muzzle brake on a magnafluxed and trued 98 Mauser action?
Keep an eye open for massacred Bubba jobs in pawn shops and gun shows. If you find a standard-length 98 Large Ring Mauser with a bolt and receiver in clean condition for a reasonable price, by all means, grab it. Or tell me where it is, so I can grab it. I have a drawer full of Large Ring 98 Mauser actions already, but I've always got room for more.