Yup, listen to cig... Try out soil first, because the hydro can get very expensive and requires a lot of attention.

Did you read this yet?
http://boards.cannabis.com/indoor-gr...-progress.html

It has a way to calculate the required ventilation according to your closet size and lights, and worked well for me.

Cig also mentioned the carbon scrubber. If you plan to fill up that space, like 12 plants, the smell will be overwhelming.

With $650 you can probably get everything you need if you shop wisely. At the hydro store, that might get you the lights, ballasts, cooltubes, and reflectors, thats it. Still need the fans and carbon filter and tubing...