Is there any farm coops?? That is one alternative source I have used. Many of your rental shops sell propane, but they are usually the most expensive. Look up your local distributor that fills home propane tanks, that should be the cheapest.
Around here, Menards started selling propane for RVs. That has been the cheapest anywhere. They are trying to build an infrastructure for propane fueled vehicles. They have different prices based on use. The operator just punches into the computer what it is for, and the amount is calculated at the pump.