-You need a ballast to run a HPS lamp.
-HIDs run hot and should ot be in proximity to flammable materials
-Batwing reflectors are so cheap it's almost funny. Check out the no-name store brand systems on Inside Sun, one of our sponsors- they're really basic beginner setups. I think I paid like $150 for my entire 400w including ballast, bulb, reflector, corset, socket. Ran that thing for a couple years and then gave it to a friend who is just learning the trade.
-I have seen cool home-made reflectors that people have made for Flourex style flourescent lamps, and my favorites involve a cafeteria-sized coffee can and a bottle of white spray paint. Go nuts. But with an HID, it's bes to do it right.