you can also lookup a local fill station on NOS-Holley's website
prices will range from $3.50-4.50/lb usually
there ARE differences betweeen the brands, but they aren't as big of a deal anymore really. i would take NX over NOS, but i'm obviously biased. if its going to be your first kit, well then imo it'd be a coin flip between NX and Zex
I had a clean install with my zex kit and it works better then ever. Nitrous = best bang for your buck hands down. Also, get a wet system. I am currently running a 75 shot on a stock block/timing... I usaully fill up at Summit Racing, and then sometimes over at my local motorsports store.. so ask around and Im sure you can find a place that fills.