Hi Dale,
I think 6k N2 is a great way to go for certain people. I have one and here is a run-down of the costs associated with it:
The tank rental is $90 per year and dry N2 is $60 per fill. With incidentals ($7 energy & fuel charge, $6.95 hazmat charge and $35 delivery charge), the total comes to $199 per year if I only need to fill it once per year.
The biggest expense going this route is a CGA 677 regulator that can handle 6000 psi and output 4500 psi to the line. I happened to have one sitting unused in my lab – otherwise they can be expensive to buy new. The local Praxair guy actually called me to make sure I had the right regulator before sending out the cylinder.
If you have one, this is a great way to go – the nitrogen is completely dry and pure. The lowest grade I can purchase is “high purity 4.8” (99.998% nitrogen) and it has only 3 parts per million water. 3ppm water corresponds to a dew point of -92F or a relative humidity at 70*F of 0.01% (not 1% but 0.01% – completely dry). You’ll never even get close to that level of dryness with any other (affordable) method. The tank they delivered is called a type 6K and it has an internal volume of 43 liters – at 6000psi that comes to 502CF of nitrogen (roughly 400+ refills of a synrod). It’s a sweet way to go for me since I had the regulator already. Anyway, hope that info is somewhat helpful.