Price of $450 on a new Ruger 77 is a good one. As to cartridge, I'd go for a .270 Win., but you seem inclined to the magnums. In that case I'd go with the 7mm Remington
Mag. Fine cartridge for all around hunting on those wide open prairies, or in the timber.
Good luck.
BTW, whatever you choose, be sure to get some practice in at those longer ranges, and
in reading the breezes.