I live in So. California, where gas is running around 10-20 cents per gallon higher than elsewhere in the U.S. Also, I assumed an average of $2.50 per gallon of regular over the past 5 years, which is probably a little conservative.
Other than very routine (and inexpensive) maintenance costs (oil change, air filters, etc.), the only other costs I've incurred are new tires and new windshield wipers, and an occasional car wash. Oh, and $8 for the DMV's carpool lane sticker.
I really do average 50 mpg because I use reasonable, economically sound driving techniques that maximize the special hybrid features of regenerative braking and deceleration.