That is like 250 + video cards LOL
http://www.bitcoinminingrigs.com/wp-content/uploads/2013/09/200-amp-3-phase-480-...-165kW.jpg
GPU mining is something that practically any nerd can do, but there are also people who aren't just dicking around with their gaming GPU, or building little crate rigs with two or three cards.
Of course, whether they'll see ROI, nobody can say. Big gamble.
It depend where you live. Here in quebec power is basically free.