I found a 96 F-350 single cab XLT, cab and chassis, 5 speed, 460 with 121,000 on the clock. The truck is in really good shape, I was just wanting to know what the truck is worth? I'm wanting something for a work truck, but
the only thing I'm worried about is the gas mileage. Just looking for your guys opinions, thanks.

Here's a pic

 

Looks nice. You are still generalizing by saying it looks really good. If the motor runs strong without any warning signs of premature failure underneath(you have to look) and under the hood, and the cab and frame are solid with no rust, it could be worth $7-8k in the right geographic.

Realistically probably$4000-5500 range, and still dependent on the bells and whistles included with the flatbed and motor. A farmer just sold a 97 tilting flatbed 250 with a 460/5spd a few towns over from me and was asking $6k. It's all about the details and how much value it has to you.

If you want good gas mileage buy a car... If you want a dependable workhorse, buy this truck at the right price.