The Astro is probably the worst vehicle in its class. It's based on a pickup truck, has a thirsty 4.3L V6, and it has horrible aerodynamics. Consumer Reports gives it terrible reliability figures. It's uncomfortable, it's slow, and it handles ponderously. The worst part--even worse than the MPG--is the safety. Take a look at it's crash test...it's unacceptable:
Find yourself a used Sienna or Odyssey; it will be safer, more comfortable, and more efficient. It will be a bit expensive, but you can expect high fuel bills and high hospital bills if you buy the Astro.