Four dollars a gallon? Put some in the post will you? Here in England it is just over six pounds a gallon, which I work out at something like ten dollars a gallon. Ok so they're Imperial gallons which if I remember rightly is a bit bigger than a US one, but not two and a half times!
At 6 pounds a gallon it won't be long before it costs more than it weighs!
Ride safe and keep smiling!