Are you keeping the dogs for hides?? If not go as big as you like.
Personally I like using my 243. I know its not that prairies, but where I hunt in SWO, it is always windy and it is flat enough to see for miles. Assuming your area is similar in description, what we do might work for you. Only a couple of the guys I hunt with will take long shots (300 - 500) and make them, and we are using 243 and 257 wby. Usually have enough power to anchor them with one shot with a varmint bullet. Match bullets can work, but sometimes don't deliver all of the energy and pass through, that is why we stick to varmint bullets.
As for a who makes them,
243: Remington (VSSF II, VLS, SPS Varmint ...... and more), Ruger, Tikka, etc.
Can usually find one in good shape used and set it up for under 1k
Just my $0.02