there are 2 types of novas. first generation and second generation. first gen. has the normal squeeze to turn on, and a switch on the back to keep it on. they work exactly like how rabbits lights do. (i prefer these for simple 2 nova conjure shows) the second gen. is most of the ones you see now. not too many people sell first. the second gen has the on, low beam (super fast flash/ dot mode), strobe mode, and sos. first gen if your lucky to find them is cheaper.
i recently picked up 10 from here.... just under $5 a pop. plus about $6 shipping.
http://www.gad-zooks.com/inova-ml.html
pricing has a lot of factors. price is determined by economics. there are numerous factors that determine how much a store sets a price at. usually online is cheaper only for the fact that they dont own a physical store, something that stores have to calculate into the price. (rednt, electricity/water, wages, insurance, etc. )sometimes stores are trying to liquidate merchandise for whatever reason. so its hard to tell exactly.