A few weekends ago, I was seeing 20# propane cylinders, new, at Wally World in Elgin for $20.00... empty, but purged and ready for filling.
Here in Austin, propane refill shops are few and far between, and tend to not bother with you unless you sign a contract of 250+ gallons per year. The U-haul places have propane filling stations... but usually nobody trained in their use is on site. So, for tanks, the closest place are the RV dealers. Propane exchanges I can find 24/7, and the clerk only has to turn a key, open the cage, grab a container with a blue seal on the end, shove the one brought in the cage, and stick the lock back on.