I just take my 5 gallon can and go down the road to where the 100 octane race fuel is only $6.99 a gallon and fill it up. Then add a gallon to every fill up to increase the octane. No way am I spending more money than that. When I lived in Minnesota, I used to go to the Holiday station in St Paul and filled up on the 100 when it was only $3.99 a gallon a few years back. Not sure what the cost is nowadays over there.