Ben Krasnow made a liquid nitrogen generator from parts bought on eBay, the parts wasn't easy to be found and took Ben over a year of searching but he proved that it can be done and the whole cost was under $500.
The device consumes about 300 to 400 watts of electricity and needs no consumables (just atmospheric air). The LN2 is produced at a net rate of about 1 liter per day. This comes out to 9.6 kWh/liter or $1.15/liter, which is substantially cheaper than having the local welding store fill up a thermos (granted the thermos must be cooled as it is filled, thus requiring more than its capacity of LN2).
Needless to say anything else except excellent work, complete info and how-to can be found here.