I did it. It actually cost about $150 per bulb... $65/each Iwasaki 250 watt, $40/ballast, $20 wiring,mogul base, reflector, and such.
I built this remarkable housing for my ballasts from acrylic with an integral cooling fan for roughly $30.
Iwasaki 250 watt bulbs are green/yellow.
Hey, hey... it was a lot better than the 4x40watt NO that I had, but not what I expected.
If I did it again, I would buy some M-58 ballasts from graybar(the ones in the page you supplie are H-370, and have my choice of MH bulbs, not just Iwasaki 6500k "greenies".
Conversly, I just replaced my 'sakis with "XM" brand bulbs that I bought form hellolights.com and they run, but the long term effects are still forthcoming; therfore, I cannot recommend them.
Bottom line, cheaper works only in the short term.