$100 DIY 150W HQI Metal Halide with eballast and bulb!
I haven't built one of these yet, but it's almost the same as what I did build in this thread: $70 DIY 70W HQI Metal Halide
The only difference is a more efficient and better looking reflector, and more power.
$49.99 BallastWise.com 150W eballast HID E-B DXE150HID1
$20.20 Astralux MH 150W DE 8KK Ultra White Bulb
$29.95 Reflector and Sockets from HelloLights.com
Grounded power cord, and a couple wire nuts (you probably already have, if not a couple bucks).
~$100 plus shipping for a complete 150W retro, and the reflector looks awesome. Plus, for $65 more you could get the ADA 8,000k bulb. 67 cents a watt!