You want to find a bulk distributer of course. Usually on the edge of towns because of the danger. It would be very unusual for there to be a good price at a campground but it does happen sometimes. Like others, I'd suggest a local Google search for distributors and give them a call.
But to answer your question, I paid $1/gal outside of Bend, Oregon last August 10th. Then 3 days ago, I paid $2.40/gal in Florence, Oregon but I should have waited because here in Gold Beach, Oregon (2.5 hours south) it's $2.15/gal. Probably because it's closer to California and there's more competition here then up further north.