A Toyota Yaris hatchback seems like it would fit your needs almost perfectly if you added a trailer hitch, altho get one with the 5 speed because the automatic is pretty much the only thing people have had issues with and it kills your mileage, but the Yaris is nice because when you fold down the rear seat it's hard plastic back there instead of carpet and it folds down pretty flat, there are a few of the hatch backs that are 4 door vehicles as well, but they seem a bit rare.
Otherwise if you are ok with a vehicle that is a bit older, check out the Saturn Station Wagon, you get alot of space in the back, 4 doors and there is one for sale in Madison for $2,000 with an EPA rating of 34mpg
2000 Saturn Wagon SW2
I like to compare vehicles off the EPA numbers instead of off "joe over there gets 60mpg with his car" because you are going to be using this vehicle to haul people and stuff and people who are not slow careful drivers will most likely end up driving it as well so they will end up getting closer to the EPA mileage.
You can also look at the EPA's web site and use their
Power Search to put in details about what kind of vehicle you need then compare them or sort them based on the MPG that they get.