How do you refill a 9oz CO2 tank for a paintball gun?

It depends on where you take it. I live in Georgia and go get my tanks filled at Dicks. In Canton the price is $2.99+tax for a 9 oz, and 3.99+tax for a 20 oz. And in Cumming it is 1.99+tax for a 9oz, $3.50+tax for a 20oz. So it depends by store but I would take it to Dicks because they have been the cheapest place I have found.