this is an old post, but some relevant info you need to consider:

I have a Waterfarm and I consistently pull 5 ounces per plant under an air-cooled hood with a 400W HPS. The plant grows to 3-3.5 feet. Ebay has someone selling 400W HPS systems for $99, but don't have the aircooled hood, just the batwing reflector. You could probably make due with that type of light, though.

So, $60 for the WF and $100 for the light. You would also need an airstone and extra air pump for about $7. And finally, the nutes that come with the WF are great, but are not enough to carry you through one entire grow cycle: you need to buy more nutes. Whether you buy more General Hydroponics nutes or someone else's is up to you. Believe me, though after the first harvest, you can sell an ounce or 2 of the weed and easily reouperate your investment twice over.

Good luck!