The price of CO2 varies a LOT depending on where you live. Here in Portland we seem to have the most expensive CO2 prices in the US. $15-17 for a 5 lb fill.
We have no local CO2 plant and this town uses a LOT of CO2. It all has to be trucked in. We have more beer brewery in Portland than any other city in the world. I do believe the current count is 42 inside the city limits alone.