Your story reminds me of a (night) cross country I did with one of my students. He had done a good bit of research and had selected a landing airport (we shot approaches at several area fields that night) based on the low price of fuel there.
It was an unattended self serve pump, with no indicated price, just swipe your card and hope for the best. The fuel ended up costing 2x what he would have paid had he gone to the 'full service' primary airport.
Moral of the story: preflight planning isn't just fuel burn & time on target calculations. If its a place you're not familiar with, get some reliable intel from someone who has recently been there. Or at least call the FBO & verify that your assumptions are valid.