Agree on the Prarie 400. Full time 4x4 isn't bad either for what you're wanting to do.

 

For that price your options are sort of limited, I'd say maybe a old sportsman 500 but reliability would be an issue and you really should have EFI for that elevation, your best bet would be to save up a little bit more and get a newer mid/big bore or maybe even buy it new from a dealer. You can actually bargain more on a new bike than a used one from a private seller. Just bought a 2013 renegade 500 for 7250 out the door. Imagine what you could buy a Outlander 400 for brand new.

 

a king quad would also be a great option the 05-08 700s have efi. irs. fits in a truck bed. quite comfy seat. easy to drive. and PLENTY of power. imho the sportsman 500s feel very slugish and heavy.