I have been running my cutting setup off a 20lb propane tank and a 80cu/ft O2 tank. That gave me about around 60-90 minutes of cutting time. The very helpful Praxair guy said that the next setup up is a 140cu/ft.. which would run for about 120 minutes and still fit in my welding cart.. but finding a 140cu/ft was not happening. So I stumbled across a 250cu/ft for $125. Recert and fill was $57.
So the math is filling an 80cu/ft bottle is $18. Filling a 250cu/ft bottle is $24. Yeah, you save a ton. 3x the torch time for 1/3rd more cost.
Here's a side by side to show you the difference:
It weights about 140lbs, and yes, I chained it to my wall.