There is currently a nitro shortage and it's driving up the cost of fuel. The more nitro, the higher the hike. People that are flying R/C heli's using 30% nitro are seeing prices of $35-$45 a gallon. The guy that makes Wildcat fuel says the cost of nitro has recently doubled. All of this is very recent. Hobby shops that have a good supply might still have the "good old" prices. If you're flying 5% or 10%, shouldn't be that much of a hike.
If you run a search for nitro methane, you'll find more info.