John,
for a 7x57 an intermediate action would be most appropriate, take small ring action if that floats your boat. 318 W-R, 3006 and 8x64S etc. requires a standard action. A 7x57 on model 21/22 Brno would be sweet

Here used actions are cheap and not very difficult to find unless you want a Oberndorf with squarebridges etc.
A Mauser action made today would be in the ballpark of 3K + Euros.

Cheers
J