Shannon sends along this tip: "cheapest gas in town is at Hertz on Hwy 20 … $2.56." Cool… I didn’t know Hertz sold gas. (Or do they only sell to customers?)
It’s also worth pointing to the Bend page on the Oregon Gas Prices site. According to that (it’s driven by user-submitted prices, and isn’t completely comprehensive), the (next) lowest price in Bend is $2.61 at the Space Age up north of town. That’s about the cheapest place I know, too.