$9? Wow you are obviously an idiot.

Use a empty 1 litre bottle ($0.05 deposit refunable)
Add sugar up to 1/4 the height of the bottle.
Add a little baker yeast
Add 1/2 teaspoon of baking soda
Add warm water just short the the opening of he bottle.
I add a little phosphate and Flourish.

Lasts a month. Total cost less than a dollar.