finding a new vehicle?

hi, ive been vehicle searching for months now, and well, i have some difficult criteria.

must have medium (23-24+ highway) to good (30+ highway) gas mileage (i'm trying to go for sort of environmental vehicles)

here's where it gets hard...

i like room, so SUV's are good,

i can only buy $20000 or less vehicles.

vehicles that have automatic transmission.

rear wheel drive and all wheel drive is also preferred.

and only cars that have 4 doors and pretty good space.

preferably something a bit tough.

i'm buying used.

toyota, honda, hyundai, gmc and chevrolet are most accepted.