Mine is like that, BUT it has a sticker on the side that says it has overfill protection. I assume there is nothing like that on the tank.
Even if it doesn't have that on yours, I would still look for a family owned place that has been around a while. Assuming it is NOT actually illegal to fill those, a family owned place is the most likely to consider refilling it. Chances are, the guy who fills tanks is the owner, has worked there long enough that he used to fill tanks like that before they had such safety devices & knows how to do it, probably doesn't like to turn away business, and knows that you will likely be a repeat customer because other places probably won't fill it for you.
Looks like Walmart & Home Depot have some of the lower prices at $43.75 (a 20 lb is actually cheaper).