Lorna is about to travel up Nawth so I am doing some online research for places for her to stop.
I began by looking up the big name truck stops, such as TA Travel Centers, Loves, FlyingJ, etc. All of them (except TA!) have a method of finding out the price of gas for each of their centers. I found a decent list of all truck stops at the EveryTruckJob.com site. Even if you don’t plan on stopping at one of them, they are a good resource for guestimating your travel costs.
FlyingJ gasoline prices
Loves gasoline prices are accessed via their main page from a drop down menu by state.
The number one thing to remember if you choose to stop at one of these places (ie a truck stop), is that you are a little fly hanging out with the bee hive. Truck stops are named such because they are, well, a place for the big trucks to stop. Some of them are geared almost exclusively to these customers. Yes, you can find gasoline pumps there, sometimes a lot of them. But the diesel pumps are what pays their bills so the merchandise inside is geared toward them. The food is guarenteed to be good and you can be entertained by wandering the aisles, looking at all sorts of 12v gear.
Truck stops are rarely the greasy spoons they used to be, especially those out on the major highway. More of them are WiFi hotspots and even have computers to access (altho usually they are reserved for those who buy 50 gallons or more of diesel).