You are paying for the bottle and the regulator mostly.
Bottles are expensive as it is, and yes, they are paintball bottles.
Mine came with an adaptor to fill it right of a c02 bottle with a siphon, or yes you have to turn them upside down if you don't have a siphon.
I recommend getting a scale, and a regular paintball fill station off of ebay, they aren't much.
I have priced regulators for the small bottles, they were ALL over $100.00.. if you can find them cheaper, let me know, as you DON'T need the kit.. but the kit I bought came with
Bottle-20oz
Regulator
Hose and fittings for airing up tires
a blow gun
a Tire plugging kit
sports ball needle
extra pop-off
I got several when they were trying to introduce them on Ebay.. I STOLE them for under $50.00 HAHA!!
I think you can get them right from Tippman Industrial, Might be $90 or so.. but well worth it.
I use mine nearly daily, it will clip to your belt too, you can use it to run an Air Nailer... cool..
Really neat setup, that never really took off, I had the rights to distribute them for a little while, but noone was really interested....... blind people..
Everyone that sees mine LOVES it, but I tell them it's around $100 and they just freeze up.. DAMN people can be tight.