Hi mgh,
This is a great time to be in the market for an inexpensive pop-up, especially for a full-size truck. I PM'ed you some craigslists posts for possible candidates in the denver-metro area.
I'm North of Denver and last year, I found one in my $500 price range. It's a late-80's 4-seasons (they were made in Denver). It's a wooden camper but I've been really happy with it. I was originally seeking a 4-wheel but you don't need one to go off-road...other campers do it well too.
I did a little work on it--mainly to undo previous owner "modifications" but it didn't need a tremendous amount of work or money to make it comfortable. All the structure, softwall, and roof and cushions were in good shape. I mainly did some wiring work, added a solar charger, and did a little cosmetic work (cleaning, vinyl tile floor, minwax on cabinets).
Your price range is completely doable, and there are more campers available for full-sized trucks than compact trucks.
I wouldn't neccesarily shop by brand, especially in the price range. I'd pay more attention to the condition of the softwall (that easily costs more than the whole camper to replace) the structure (no soft spots) and the amenities.
I'm not sure if your truck is a shortbed, but mine is and I'm really glad I ended up with an 8-foot camper that goes to the end of the tailgate. That way, I get a storage closet, a longer countertop with 3-burner stove and double sink, and stretch-out room on the lower bed.
Let me know if I can help--I love talking campers.
Eric