The best way to save money on propane exchange is to forgo exchange in favor of refilling tanks. Exchanged tanks are often under-filled in relation to their capacity, meaning the consumer pays more money for less propane.
A propane tank can be refilled as long as it is still certified as structurally sound enough to hold propane under pressure. Certification lasts a few years and can be renewed by refilling companies, but tanks with expired certification can generally not be refilled in a retail setting. In these instances, exchange is best, as it allows the consumer to receive a new tank.
Exchange rose in popularity because it is easier for retailers. They can simply keep a locked container full of tanks outside the store, and exchange them whenever a customer desires. Refilling a tank requires special training, meanwhile, so it represents a bigger hassle than exchanging.
Exchanging is more expensive for the consumer for two reasons, however. First of all, most people only own one propane tank at a time, so many people end up exchanging while there is still propane in the tank, wasting propane they have paid already bought. Secondly, exchange companies now only fill tanks to 15 pounds of propane, despite the fact that they can hold 20. Refilling instead of exchanging can result in significant savings for heavy users.