Before we got out of the propane fill business completely, we went to a $10.00 minimum. Otherwise, we would have someone wanting to top off their tank on the coldest, wettest day of the year. Of course it would be a class C or VW campervan where getting to the fill required crawling on the ground and contorting our bodies in ways the human body should not contort. Then we would find that the rig took exactly 2/5th of a gallon. Just wasn't worth the effort for eighty cents. Hence $10 or no gas for you.
Even with that, it didn't take long for us to decide it just wasn't worth the pain and effort to dispense propane at all. Haven't regretted that decision for one second.