My Wee-strom gets between 42-47mpg...not the magical 50mpg that you see people talking about on the internet. I always run my fuel budget based on the US average price. Locally, I typically pay much less per gallon since we live closer to some refineries in UT and WY, but 200 miles away in Boise the price is often 15 cents more per gallon.
Average US gasoline price today is $3.37 USD per gallon. 4000/45mpg*3.37 = $299.55.
Gas prices run higher in the summer, but today's average price is really high for this time of year (locally, I'm paying $2.89 per gallon).