In that price range, you can forget about any Japanese minivans, you would have to go domestic. The best of the domestic minivans has always been the Dodge Caravan. It has been by far the most reliable domestic minivan. Also, try to find one that is '96 and up with the 3.3 L V6 (apart from the 3.8 L) because they are bulletproof; I have a '96 Plymouth Grand Voyager (twin of the Caravan) with the 3.3 L with 300k kms, and the engine still runs great.
Good luck!