nitrogen is a common misconception. its really compressed air, or hpa (high pressure air). sure u could use nitrogen, but theres not that much more of a benefit although it is a more stable gas. if you think compressed air and co2 are the same thing, u shouldnt be playing ball.

and 4 dollars for a 68/4500 is a ripoff. get your own fill stations, and two tanks to top off, and ull be paying a few cents for a full tank.