I say just get something that gets ~35+ mpgs. If you're gonna do it, do it right. I had an '05 CR-V (hated that little POS) for a DD for a while. It only got about 23 around town and my 4runner gets ~16. It just wasn't enough difference to justify a car payment.

Although in my case, I bought it from my sister for cheap so I sold it and made ~$2500 on it almost a year later. She wanted to trade it in and I bought it for what the dealership offered her. My next DD will be a ~'99-02 standard cab 4x4 4 banger Taco. The gas mileage isn't great on the Tacos, but I would be buying it for hauling stuff around, not so much the mpgs.