I beg to differ about a custom costing more than a factory.
My 9.3x62 cost:
75 dollars for action
789.80 for parts and labor. Lothar Walther barrel (and installation) backup irons (and installation) and manganese phosphate finish.
I had a takeoff stock from another project, so no added expense there, but m98 stocks are readily available.
If you include the 25 dollars FFL fee for buying the action that's a grand total of 889.80 for a custom mauser. Going with a bigger caliber wouldn't change the cost.
That's still over 300 dollars less than at $1200 new factory rifle, and I got to specify barrel length, contour, and metal finish.
I can't recommend the gunsmith enough, Mike McCabe http://www.mccabeguns.com/