1 Imperial gallon = 4.54609188 liters
1 US gallon = 3.7854118 liters
Due to us being metric in the UK we pay for gas by the litre, so it current is $1.7 a litre here.
So that would be about $6.47 for a US gallon, but that isn't really a lot, normal price, and the fact that British cars are more economical helps. We have a 1.6 Dis, Turbo, which averages 80-90 miles per gallon on the motorway.