If you're hauling, I'd go diesel. Added load can cut a petrol powered truck's mpg in half where a diesel my only lose 1 or 2 mpg.
I don't think you'll find a toyota in your price range, but those are good small trucks.
A hardbody Nissan pickup can be had for cheap and the motor is pretty torquey for a 4cyl. I had the motor in my 240sx. It lacks top end, but has a very nice low and midrange.
When you're not hauling, you should use a bed cover and other aero like this:
Click the image for more info. The Cd was cut almost in half and is now equivalent to that of a Honda Insight.
Matt