Used to be the cheapest gas in GF was always at Sam's Club because, with apologies to the GOBC, no one dared oppose the Grand Forks gas mafia led by a local station owner who shall remain nameless. Sure they don't wanna hear it but there's a new kid in town at the TA Truckstop on Gateway at I-29. They're at 2.63 a gallon while other prices around town vary up to 2.90. Even Sam's was at 2.74 - 11 cents more expensive.
Funny part is the aforementioned "boss" happens to have a station across from TA so they have to sell it at the same price (2.63). Another one of their company stations farther down Gateway was at 2.84 - 21 cents a gallon more expensive a mile and a half away. So if you're looking for the cheapest gas in GF head to Gateway drive.