For what you're looking for, you got 2 good options in my opinion:

1. 2005 or 2006 Toyota Tacoma extended cab or double cab, V6, 4x4 with low miles. You should be able to find one in the 23K - 25K range. You probably won't get 20mpg, though - figure on more like 18 average.

2. 2005 or 2006 Nissan Frontier extended or double cab, V6 4x4 with low miles. Pretty comparable to the Toyota although you may get slightly worse gas mileage. If you can find one where you live, it'll probably be slightly cheaper than the Toyota as well. I used to have a 95 Nissan 4x4 that I really loved - great truck that the salt from driving in the rust belt states took its toll on and I had to get rid of it.