Not including start up cost, just the recurring costs, power, soil, nutes and bulbs etc. It costs an avg of $20 an oz, it costs $30 a month to run a 600w mh/hps so $50 for a thousand watter. It costs $35 for a big bag of promix bx which almost exactly fills 6 7 gallon smart pots. It costs $3 a week in nutes and if you wanna replace the hps bulb every cycle that's $36(I know I'm a cheapo).
So theres $115 a month I usually end up with 8-10 oz over the 2 month flower period so actually it's more like $23+ per oz, I have every last penny in the notes on my phone it works out to roughly $20 an oz. That's growing with a 600w in a 4×4 tent. I'm doing two one thousand watters and a vertical 600w next time in an open 10×12 room so I hope to get a much bigger bang for my buck.