Because for 200 watts more [not that much] and a price difference for 50-100$ you are able to increase your lumen output by 40% or so. I mean 95,000 lumens is alot more than 58,000. You are going to be able to grow bigger, denser, better buds because the light is putting out more lumens.
Digital ballasts are very efficient, and the energy cost between a 400watt - compared to a 600 is a couple dollars a month. Look at it this way. a 400 watt is more like a big 250w. and a 600 watt performs like a small 1000watt.
Fan - hardware store. 6 inch inline duct fan 250 cfm= 30$
the ducting will run you like 15$
speedster - speed controller for fan
Reflector - Yieldmaster II - 110$
ballast - galaxy 600 watt digital [ green ] 250$
digilux bulbs are about 100$, i highly suggest starting with the MH, it is the best bulb on the market IMO, and spectrum is THE BEST, hands down, no questions asked.
SERIOUSLY what hardware store you going to. 250cfm inline for $30. this is a serious quetion not being a jack ass thanks