nothing in your price range is going to get 20 mpg while towing. you probalby won't be able to find a v6 tacoma or 4 runner in decent running shape with $3k.
A pathfinder maybe, they are rated to tow 5000 lbs but have very soft back shocks. Mine is an 02 and its got the 3.5 and it will tow a 2000 lb uhaul car transporter with a 3000lb car on it no problem at all, 70 up hills, etc.... but the older ones (like pre 99) that will be in your price range had the 3.3 liter v6. Its a turd. Neither engine will get 20 mpg highway anyway.
Isuzu rodeo/honda passport (older body style) had a lot of reliability problems and just are not very comfortable vehicle, in my opinion.
I think you would be best served by a 2wd mid or fullsize truck. You can find a used fullsize chevy 1500 or ford f150 work truck edition regular cab, late 90's or possibly even early 00's, with a v6 and automatic and AC (manual windows and doors, vinyl floor, cloth bench) for your price range, with low miles, and they will tow what you need to tow with no problem (and still have the bed for spares). Trying to find an extended cab will jack the price up a good bit.
I'd probably avoid an S10, ranger, or the like, as they are not rated to two what you need to tow without the larger engines and automatic trans and that generally jacks the price up to what a fullsize would cost... and you are still looking at towing a car with a small truck that doesn't weigh much more than the car. The compact trucks just don't have the right equipment to tow a car ona regular basis/over long distances. Especially when you figure 2000lbs for a car trailer, youre looking at over 2 tons behind the truck... a ranger extended cab weighs in a good bit less than that (and doesn't have the cooling or braking to support 2x the weight).
I like the minivan suggestions... I had an astro and it was very nice, and they are really cheap. They have their quirks but its a practical vehicle you could sleep it. 20 mpg is a pipe dream tho. The FWD minivans might get better mpg but probably wouldn't tow nearly as well, especially not in slick conditions.
I'm pretty confident if you find yourself, say, an F150 work truck, you could get something with under 100k miles, v6 engine, auto trans, for your price range.
If you go back a generation and look at 96 and under trucks, the I-6 is known for its extremely long life... 200k and beyond are common. I've seen this engine in 250's and 350's towing 8000 lb loads. Its not gonna go 65 up the hills, but it will do it.