well if the person is smart and they are doing this in a small area, then they probably have vented lights. Now, how much light you need depends on how much you can use. If you have CO2 enrichment upto 1200 ppm then you could use something more like 70w/sqft. You'll also need nutes, if any one of the three are suboptimal, then you will have poor results, and you will be wasting money. If they are all equally bad, and you make shitty quality, and you sell if forr dirt cheap, your still making money (not the best way to go)
My advise is to pimp your growroom, then you will capitilise the highend market and be pretty happy.