Building my first pc case cost me about $100 total. I yield > 1 oz. per harvest out of it every 3 months. That's plenty for me to smoke. If you have $300, you can build 3 cases for an oz. per month. Easy math, for me...
Also, I should mention that it's pretty cool to have people over.. working in the house or whatever, stand 1 foot away from growing pot and have absolutely no idea.
~ER~