So, I got to thinking that there might be a better place than AGL, Praxair or Aigas to get the nitrogen or Argon. A couple of minutes with google turned up a welding supply / gas supply about a mile from my house. They will rent a 330cf cylinder for $4.00 per month and fill it with nitrogen for $29 or argon for $65.

This is way cheaper than I would expect to pay at any of the big shops, and couldn't be much more convenient. A huge bonus.