This is a really tough request. A truck or large SUV sounds like the best bet for your desires. The newer models may give you good fuel economy ~ 25mpg highway, but these are way above your budget. My next suggestion would be a minivan - again sounds like you tried this approach.
So my suggestion is 2 vehicles. 1 for work, and 1 for family.
For work look for the most fuel efficent car that you like. A high milage gen 2 prius, ~05 can be had for around $4000.
For the family car an Explorer is a good choice, but maybe look for a model from a dead brand, such as Mercury or Saab.
For an off the wall suggestion look at the Mazda5 - they aren't large but seat 4 comfortable and and a large trunk, as long as the 3rd row if folded