To the OP,
It depends on what you're looking to do with your K31.
If you're buying the K31 to shoot for fun, buying one from Allan's Armory for $200 will be fine.
If you're looking for higher quality/collectible quality, Simpsons is the place to get it. It will easily cost you +$350 and much more.
I've bought from AA and Classic and both are good vendors.
Good luck and enjoy your new K31. Time to start saving for reloading supplies for the 7.5 Swiss.