When driving at higher altitudes you can use fuel that is lower octane than is recommended in the manual. Saving $4.00 per fill-up is not as important as keeping a vehicle running properly. I find that when I use mid grade fuel my gas mileage drops, sometimes considerably. The same goes if I get E15 instead of E10. When traveling sometimes I can find No-Al stations this will really increase power and gas mileage. Since most of my travel is by motorcycle both work and pleasure I run into many different types of fuel. One of the worst was in Kansas where I had been getting 250 miles between fuelling's, a tank of what ever it was dropped my range to just over 100 miles. The other was in Hanes Junction, Yukon where the Shell station was selling Benzene instead of gas. This really screwed up some motorcycles and killed gas mileage.
I find that when traveling the most important way to save fuel is to keep a smooth and steady speed and not speed. It also helps to follow someone. This year when traveling with in a group I was getting 55mpg on my BMW K1600, when traveling at speeds faster then what was posted the mileage dropped to the mid to high 30s.