Remember that Halon and Halotron are not the same thing...
Halon exists only in limited quantities now as it's against EPA regs to manufacture more, so the existing supply is all there will ever be, and once it gets used on a fire it's gone forever. It's expensive to buy for these reasons.
Halotron is a substitute that is more environmentally friendly and still legal to manufacture, and is supposed to be nearly as good at extinguishing fires. I don't know specifics, but there is plenty to read on the web if one is so inclined.
All I'm saying is don't buy one and expect the other.