I think the most economical way to build a high-quality sporterized Mauser is to search out a JC Higgins Model 50 or 51 rifle. These guns were sold by Sears and a few other catalog outfits and were assembled in the US on commerical FN 98 Mauser actions. The FN actions are some of the finer 98's available and are drilled and tapped for scopes, bolts are turned down so they clear scopes, do not have the thumb cutout for using stripper clips, and the list goes on. Model 51s have hinged floor plates with inside the triggerguard release levers a nice feature. Another option are the Zastava mausers found in Interarms Mark 5, Remington 798, or straight Zastava's, these are qute nice guns for the money.
The cost of gunsmith work is much more than it was than in the heyday of sporterizing military weapons and the cost of the weapons themselves have gone up dramatically, the combination have made starting from a military Mauser to be a money pit. I know I have done both, I still do some sporterizing of military 98's as I have a bunch of receivers laying around and the most important the machine shop to do the work.