Seems like the most recent refill on my 100 pounder was a little over $50.
Dan, as far if the 100 pounder is better, I guess it's relative to your usage. Back when this was all just for fun the 20 pounders were fine. I kept three of them.
As you get more serious and are doing more forging, the 20 pounders start to become an annoyance. Long before the tank is actually empty, the efficiency starts dropping off, the outside of the tanks start frosting over, the forge starts spitting and sputtering, etc. The 100 pounder is like the Energizer Bunny. It just keeps going, and going, and going ...
As a full-timer the 100 pounder is a necessity for me. I do still have the three 20 pounders that I can use for emergencies. For example if I fire up the forge on a Sunday and run out of propane, I'll hook up one of the 20's to get me through the day. Then come Monday morning I haul the 100 pounder in for a refill. I love the thing. It's well worth it to me.