RE: Sub $400 .300 Win Mag
The last two posts are very good examples of good advice as well. The Remington SPS and Tikka T3 Lite are two very good options although I give the nod to the SPS because Remington is about as American as you can get!
Remington, Ruger, Savage and Tikka are all very reasonable options. BTW, the 710 is no longer in production, it was replaced with the 770 or something like that.I don't know about it, but if the barrel can be replaced on it, it might not be bad either. Otherwise, stay away from it also.
Good luck