To make liquid nitrogen, you need an special equipment. Imagine that it's like a refrigerator, but more complex. So to run the equipment you will need a lot of electricity.

You have to do the calculation of how much will it cost in electricity to produce the liquid nitrogen necessary to have the same impulse of the usual fuel.

Also, liquid nitrogen is very cold, mixing it with water will make a lot of ice [1]. The ice is not good for the nozzles or whatever is in the "engine" of the jet.

[1] Liquid nitrogen is quite cheap, something like $3 per gallon. You can get some for free in the laboratory during a major degree in Physics. It's nice to play with it, but be careful and follow the safety instruction. :)