you're on the right path with a cherokee (XJ...old body style) with the 4 liter inline 6. arguably the most bullet proof engine ever made. don't be scared away by high miles, those things are ridiculous. you should be able to pick up a 99, 00, or 01 for under 5 grand no problem. gas mileage is the only real issue. expect to see about half of what you go with your sentra. 14 city/ maybe MAYBE 20 hwy is realistic
another option which you should really consider is a subaru outback. Super reliable engine as long as the headgaskets have been replaced (and almost all of them have) they kick ass in the snow, have plenty of room inside, and are good on gas. just about everything you need for a mountain ride. expect to pay about as much as you would for a jeep of equal year and mileage. honestly its your best bet for a mountain cruiser.
my girlfriend was just in the market for a new ride and oddly enough those were the two cars we were looking at. she ended up getting a 1999 outback with 120,000 miles for $3500. the car is awesome! I'm a german car guy all the way, but these subarus are built very well and made for the winter. awesome awd, heated seats, heated mirrors, heated windshield wipers, roof racks, cargo space, and comfortably fits 4 adults with enough gear for a weekend.