You can easily get under 10 cents per charge. I use Pyrodex P. It is unregulated and a bottle will last years. I assume you have an altimeter that will trigger the charge. I use this methos for both the drogue chute at apogee and the main chute at 300 feet.
This is so simple, but it works. I use a 1/2 cpvc endcap with a hole drilled in it. I glued a holiday light (xmas light) receptacle in the hole and have it wired to the altimeter. I then use the bulbs with the tip of the glass sniped off. Insert bulb, fill with Pyrodex, then tape it up.
It doesn't yield a large "bang", but that is not what you are after. It does generate enough expansion to pop the nose cone and shear the pins.
I have yet to have a failure.
Xavier
