hey sky, If you go with NOS and all the trimmings, it is going to run you more than 500.00 My setup cost over $1000 and I still need to add a few things (bottle pressure gauge $40, a purge kit $95, and a spare bottle $150) I really dont mind the refills but you did see the downside last time we went to the track when I "purged" mine
Nitrous is fun but it is not as cheap as everyone thinks it is... the 75 hp kit is around $450 and the stage two kit is around $695-$795