I am sure the price was posted last time I was there. Too high; I didn't buy any.
I encountered very high prices in northern Saskatchewan (north of Lac La Ronge) where they had the same setup - a relatively small tank above ground, obviously operating with very small volume. These locations probably aren't served by the big company tanker trucks. They may well be offering a sort of emergency only service at cost rather than trying to make money. When I think of it that way, I very much appreciate it. Note that the Columbia Icefields Discovery Center doesn't bother to supply fuel to its thousands of customers. Maybe you could score 5 gallons if you were desperate, and happily pay $50 for it.