http://www.capecops.com/newsroom/2011/4/12/cape-coral-police-vin-unit-busts-grow-house.html
That link describes the bust a little better. There was a "total" of 39.5 pounds seized from those plants. When they weigh out the weed to get the value, they weigh uprooted right out of the pot; roots, leaves, and everything in between. So in all reality - with their estimations - each plant had a value of $5063.29. Either the cops just decide random values for the marijuana they seize, or he was growing some 50% thc marijuana. Hell, I'd doubt if it even actually weighed 39.5 pounds... from the looks of the pictures they were pretty skinny and lanky looking.
I'd be curious to see what would happen if I was growing 50 plants of some ruderalis hemp and then purposely got the house raided. I bet anything that they'd give it a value of close to $250,000 when it'd be worth no more than $100 total "street value" due to it's inability to get you stoned.