When they say "street value", they typically mean "as sold in smaller quantites" as opposed to wholesale values. It appears here, they may have simply determined the value based upon a 1/4 bag selling for $30-$35. $30 x 4 quarter bags = 120/oz. $120 x 16 = $1,920 per lb.
They never use wholesale prices because the ignorant public equates higher dollar values with a more devious person who mus be thrown in prison to protect all of society.
Everybody's happy.