I use Nitrogen from an airtank. I paid about $80 for the regulator and a full tank. I rent the tank from a welding supply shop for $9 plus about $13 to fill it a year. It may cost more from a diving shop. You want to lease the tank because they cannot refill a tank unless it is tested and certified first, and a test costs about $100.00. So they lease a tank to you and they take care of the testing. Kinda a good deal. A tank can last about a year or two depending on how much painting you do. You can also get just about any size of tank you want since Nitrogen is quite popular.