If it would work,depending on what type of ignition system you're running, have you considered putting in something like the MSD adjustable timing control? I was having some pinging problems with my engine after a rebuild a few years ago unless I mixed some 110 octane race gas with the 91 pump premium. After I installed the adj. timing control I can dial in the necessary retard on the fly whenever I start to get pinging on straight 91 octane. Works great when there is no 110 race gas where ever you happen to be. I really can't notice much change in performance and the car doesn't diesel when I turn it off when it's retarded a few degrees with the control. If I later throw in a little 110 I can just dial my advance back up. To answer your original question about price on higher octane fuel, my supplier of the 110 octane pays the going price when he fills up his tank & that will last him 2-3 months depending on the time of year it's purchased. I expect his next load will be cheaper than what he has in the tank today because he had to fill up when gas prices were high. Hopefully, the next load will reflect the lowering in gas prices. FWIW.