I spend about $40/month for my 300W of CFL & ventilation. My hardware is mostly slalvage, bulbs were donated by a stoner buddy at Home Depot, and I've spent mebbe $$75 on soil, mylar, and worms. I get about 1.5 - 2 oz/plant. One or 2 plants per run. So for me, it defo pays for itself.

And I know I"m going to have to start changing out some of the older bulbs in the next grow or 2. (A CFL is good for about 5 grows)