AtlLaw:
I agree about the 1909 Argentinian being one of the nicest Mauser's for a custom build, but they are getting harder to find at a decent price. Even nice VZ 24's are getting harder. The Mexican Small Ring is very difficult to find and the G44/33 is impossible unless you spend thousands. You are correct about being cheaper buying a commercial rifle. The fact is, even if you find a good deal on the donor Mauser and even if you do most of the work yourself after you clean up and square the action, do a bolt handle job, install commercial shroud and commercial trigger, buy a commercial barrel and stock it does NOT make economical sense to build a custom Mauser. You can easily find "custom" Mausers on Gun Broker for less money than doing the above. But that's NOT the point, is it.
Huffmanite:
The 7 x 57 is a fine deer cartridge and IMHO, mostly over-looked these days. I tend to like the old "classics" like the 7 x 57, 257 Roberts (based on the 7x57) 6.5 x 55, 35 Whelen, 220 Swift, 218 Bee, 22 Hornet, etc and have rifles in all of them. The 250x300/250 Savage falls in that category and one of your gunsmiths should have easily been able to offer that caliber. They could have reamed with the very common 22-250, then opened up the throat with any 257 reamer or rented a 250 Savage reamer.
Happy Hunting!
D