Ford still makes the Ranger in long bed form - seven feet versus the 5.5 foot bed. However, you can only get it with the 4.0L engine. With the auto it'll make a good everyday workhorse with the 3.55 gears as it'll tow upwards of 5.5-6K.
Keep in mind that for four cylinder trucks with the manual transmission tow ratings are greatly reduced over automatics, in some cases up to 2K. Ford ranger with the 2.3 and manual transmission is only rated around 1500lbs. Depending on the weight of the trailer and your equipment, you might be cutting it close, and as mentioned, a V6 would be better suited as the 4cyl will have to work harder than a V6 to get up to speed.
I know you're after a truck in the $6K range, but for $300 a month or so you can get a decently equipped long box Ranger with the 4.0L V6. At least that would be my move if I were you. Then you don't have to worry about previous history, or getting into a vehicle for a test drive only to find out that it STINKS and wasn't kept up at all. In the end you'll get what you pay for so shop around wisely.
I'm fairly certain that the older S10 was offered with a long box and the 4cyl back in the day, but the trouble will be with finding one in decent shape.
Mileage is calculated in several ways, the major being WEIGHT. The more a vehicle, or combination weighs the more fuel it'll take to move it. A lot of folks never think about the driver. In a light duty truck, a driver weighing in at 150lbs will get better mileage than a driver weighing say 350lbs! Be sure to think through all options before you decide. I wouldn't necessarily look at price, I'd be after maintenance history on a vehicle that I'm interested in.