I'm in the process of converting my fluorescent setup to metal halide.
here's some good info people gave on
my thread:
mine is an old nuarc light table that i chopped up in order to put stronger lights in, but i'm getting to the point where i need a single light source.
i bought a MH bulb on ebay for $1 (hope it works!!!) and a ballast for $65, shipping and all i've got about $100 in it. you'll need to build the structure if you don't already have one. check out the one in the thread, it's really nice for a home-built one.