Around here Coleman fuel is a touch over $20/gallon.
It is low octane (50-55) and has no traditional gasoline additives (which is the main reason people use it), but is apparently very hard on the valves when used as a motor fuel. I've seen that engines tend to run pretty hot using Coleman fuel. Mind you I'm talking about 4-cycle scooter engines (not model engines and not Simplex engines, but still...). I wouldn't use it, personally, as I think there are better options for similar money. Those that really think running Coleman fuel sounds good can probably buy non-Coleman branded naphtha for half the price through a paint store or similar.
I think one of the big problems is ethanol.
Modern gasoline blends, most of which contain ethanol, are garbage. The stuff has virtually no shelf life and is very hard on gaskets, seals, fuel lines, and the like. The ethanol blended gasoline of today is also hygroscopic, meaning they will absorb moisture from the air and you'll end up with water in the gas tank eventually. In a car that is driven all the time and was engineered to use this kind of fuel, it's no big deal. In an antique, this stuff causes lots of headaches.
The only way to defeat modern fuel is to not let it sit. Run it ALL out of the system and drain out any used fuel when you're finished. It's still hard on your machine as you're using it, but at least you will minimize the risk of the fuel breaking down and gumming things up.
I think that the best thing to do is search for non-ethanol gas, race gas, or AV gas. Race gas (from a drag strip, for instance) isn't cheap, but it's designed for use in gasoline engines and is ethanol free. AV gas (either blue or no-color grades) is probably the best thing, but it's hard to get unless you have a small scale airport near you that's willing to fill up cans for you. Often times they want a tail number to associate with the purchase. Since I don't have a plane, that's kind hard...
Look here:
http://pure-gas.org/
