In my part of the country, new OPD tanks are costing $23- each in pallet lots. Propane costs the dealer 75.9 cents a gallon. There are 4 gallons of propane in a 20# tank.
Dealers can refill non OPD tanks if they are used for welding, forklifte, or propane driven machines like floor buffers, yet most dealers refuse to fill tanks because they make more money selling OPD tanks. Many if not most OPD tanks won't deliver enough gas to keep an engine running on a floor buffer, but propane dealers don't care, they are making big $$$ selling new tanks.
NFPA section 58 was written with the exclusions for good reason, feel free to tell the dealer the tank is for your welding torch or floor buffer and insist he fill it. If he refuses, haul his [censored] to small claims court.
OPD valves are pure government BULLSNOT, given to us by the AlGore idiots who hate internal combustion.