Just did some quick math... This isn't exact as I haven't saved every Airgas receipt, but I have saved most - some time ago I wasn't all that organized and usually tossed them on the floor of the car, then they'd get put in another stack sometime at a later point. The receipts I do have go from March 2011 to last week, though some in between are likely missing, as well as the ones prior to March 2011.
But, with what I have this is the numbers I crunched...
Liters of LN2 billed: 1,653
Price including Tax/Hazmat: $929.80
Price/Liter: 56 cents/Liter
Not exact, but damn thats a lot of LN2 at a pretty good price.
At my new airgas location, with my current dewar, I am billed for the following every trip:
Liters of LN2: 150
Price including Tax/Hazmat: $86.01
Price/Liter: 57 cents/Liter
However at this location, they typically don't give me 150L unless I tell them to at least twice. For whatever reason, they have a hard time filling a 150L correctly, so they usually default to giving me something like 100-120L and my gauge isn't all the way to the top - when I tell them to fill it all the way (I have already paid for it at this point), they act annoyed but do it.
Typically lately when doing GPU and CPU at full pot, 40-60L lasts me for a full session 4-8 hours.