Google: DIY reef
and check out the MH retro kits. You can buy an IceCap retro(400w IceCap ballast-one of the best brands you can buy, mogul socket with cord, and spider reflector) for just $200. Then throw in a 400w (10K or 20K) XM bulb for $63, and you spent only $263 and will have a top notch MH system, not junk like I'm betting that deal is.
There is a huge difference between brand name MH and knock of MH. So it all depends on the brand name of the set up you posted. If it lists no name for the parts, and only says 400w MH ballast and 400w MH bulb-it's junk.