I don't know what the availability of diesel is like in the US (probably a PITA like Canada) but you get a hell of a lot more miles to the buck!
It's readily available at most major gas stations - but priced significantly higher
per gallon than gasoline/petrol. Where I live, regular gasoline is averaging about $4.01 this week whereas diesel is running around $4.36. Looks like the US oil companies noticed the increased mileage and adjusted their price for diesel fuel accordingly.
It's more expensive in the UK but nevertheless it is still cheaper in terms of mileage.
My Peuoget is costing me between 10p and 11p per mile (unless the weather is really bad when the cost goes up for all vehicles) to run but my partner has a much smaller petrol car (considered to be so fuel efficient the government gave her a subsidy to buy it) and yet it costs her between 14p and 15p a mile to drive.
It is just a fact of life that a good fuel efficient diesel will give you a lot more miles to the litre/gallon than an efficient petrol engine (unless you are prepared to drive a two seat Smart Ka) - so even with the price differential it is still considerably cheaper to drive diesel.
I presume those prices are per US gallon? That works out at $1.15 per litre for diesel - in the UK that would cost £1.46 per litre (ie. $2.22 US) which is why I am paranoid about getting the best mileage I can.
At the end of the day all cars cost a fortune - a good rule of thumb is that the total cost of running a car is about twice the cost of the fuel you put in it (at least in the UK) - so with price differentials it looks like in the US it would be more like 3 times the cost of the fuel. That is assuming you don't buy a clapped out old banger that costs a fortune to keep running at all.
If I lived/worked in a city with decent public transport I would just hire a car when I needed to - a lot cheaper - and use public transport. Unfortunately in the area I live public transport is completely impractical unless you are retired or not working and able to plan your day around the infrequent buses.