I've got a nice brownie-making system going. I use 2.5 (dried) ounces of good pot per 48 fluid ounces of oil. So, figure that bottle costs about a thousand bucks on the street, and it's good for around 11 pans of brownies. A dose is two brownies, and the pan is cut into 16 brownie squares, so a pan is 8 good doses. That means the bottle is good for about 88 strong doses. Divide $1000 by 88 doses and you come out to about $12 per two brownies. That's assuming that you use something high in quality for the 2.5 ounces (I used White Rhino, which costs around $400/ounce on the street when you can find it.)
So, the question isn't how much per brownie, but how much per dose, and a dose can be one or more brownies, depending on how much (and what quality) of pot was used to make the oil or butter. I wouldn't pay more than ten bucks per brownie, or more than twenty bucks per reasonably strong dose.
"Before you consider one an enemy, first walk a mile in his shoes. Then, if he *is* an enemy, you're a mile ahead, and you have his shoes."