O2 or N2, put whatever u find convenient. Both should work equally well for the purposes you guys will be using the car.
Found this on the web. Hope it gives u some idea.
How much does it cost to fill tires with nitrogen?
The average cost to fill a tire can vary widely, anywhere from $3-10 per tire, depending on several variables such as tire size, tire pressure, and if the dealer chooses to bundle any other services with the nitrogen fill. This cost usually includes top-offs for as long as you own the tires. Some retailers don't charge anything if you purchase tires from them.
To find a nitrogen dealer near you, just enter your zip code into our Nitrogen Dealer Locator
. This will give you a listing of all the dealers within 100 miles of you, along with contact information for each.