Sorry to hear about your bad luck with the S-10 with the Duke. In my experience the Duke is never going to set the world on fire but it's as reliable as a stone ax and almost as sophisticated. Ours was bulletproof when we had it. There must have been something seriously wrong for yours to let you down like that.
Looking for an economical truck, I'm inclined to tell you to set your sights on the 80s. There's somebody on here with a newish
Canyon and he's pushing into the 30s with his mileage, but the more modestly sized compact trucks of the 80s - when they were still compact - can really deliver on the mileage front. Five speed manny, 4-pot engine and no frills. A relatively lightweight, uncomplicated box into which you pile your junk and take it places.