AVGAS is special. It comprises only a tiny fraction of the gasoline sold in the US each year, and must be specially formulated. Of course a rise in price of the raw material (crude oil) is going to cause the price to jump, but I would never expect it to come down much.
We are lucky that anyone even makes the stuff anymore. As more airplanes convert to diesel/jet A engines the demand will drop further, resulting in decreased production and even HIGHER prices. The refiners don't need GA or AVGAS...they almost do it as a public service.
But there are many other costs associated with GA...Mx and liaibility are the biggies. I wouldn't expect the cost to come down...the transition to diesel engines will drive costs even higher (the retrofits will be expensive).
If you're gonna do it, may as well get started because it's not going to get any cheaper...