400 watt metal halides

I found s person selling two 400 watt metal halides withthe 2 reflectors and ballast/timer that where in the canopy of a tank he bought..it is an excellent excellent price..but those of you who have experience with metal halides let me know...its for a 220 tank..is that going to be outrageous power bill increase...if i mount them in an open back wood canopy top will i need a fan or is that not enough..pleae anyone who has experience and is in the know about these fill me in about pro's and cons etc...75 dollars..all in working order..sounds like a deal to me but i worry about the heat..I dont care if it made my power bill 10 to 20 bucks more but if we are talking 50+ def something to consider.