No, not at all. They don't sell low octane fuel cheaper to save YOU any money, they do it because people will pay more for gas at the pump to get a lower price. The difference in actual fuel economy more than offsets that difference in price, and they know it. Haven't you ever wondered why your car doesn't get nearly the kind of mileage that they claimed that it would on the sticker it had on it when you bought it? The auto industry knows damn well that your fuel economy depends on the quality of the fuel you use, so they use 100 octane aviation fuel when they do their tests. Av gas has to be made to higher standards, and better consistency. But again, you don't have to spend $10 a bottle on fuel booster, it's just naptha, and mothballs will do the same thing. More octane = better mileage. But they don't give you any kind of real indication of that on either end. The price you see at the pump means nothing, and the mileage your car gets means nothing, until you do all the math yourself. Fuel economy donsn't measure dollars per gallon, or miles per gallon, it's about miles per dollar, and the only way to calculate that is to do it yourself. And I have, so now I believe.
Gasoline is only about 10% efficient as a motor fuel. That means that for every 10 btu's of energy created when you burn it in your engine, 9 go out the radiator for every one that pushes your car down the road. So it really only takes a 5% improvement to manifest as a 50% improvement in fuel economy. Even injecting a small amount of water into your intake will do the job, that water will use some of that heat to convert to steam, more pressure to push the piston, and less heat. The reason that is unpractical is that it will rust the inside of your engine in no time. But this was done quite a bit by the loosing side near the end of the war, when they had a huge shortage of fuel, and could afford to replace the engine after every flight, that is, if they came back at all, which they usually didn't. Mothballs will give you about 5%, which always translated to a 50% improvement in fuel economy EVERY time I have tested it, or had anyone else do so to convince them. Your results will be a bit less if there is ethanol in your fuel, though. This only applies to the gasoline content.