Assembling a HPS?

Went to homedepot 2day and found 400watt hps bubls for 21 dollars. i was wondering what i need to buy to assemble my own HPS setup. anyone can show me the supplies taht would help

If you live in the states check craigslist. I get the old "high bay" lights (make sure there switchable) For like 25$ each . I just got 2 1000w MH's with bulbs for 50$ total . Picked up . I just add wire from the ballast to a plug (the wires should be marked you want the 120 one and the 2 other wires that are diffrent green and black i belive) Then add wire to the mogul side . to extend it to a good hood.

Thats my secret to cheep lighting. Generally you can find 400w and 1000w for a good price on there tho. With bulbs, Heck theres a guy right now selling new 1000w bulbs for 10$ a pop around here .