I recently won a Helios 400w HQI electronic ballast on eBay, and I don't know exactly what HQI is but I guess that it has something to do with double-ended lamps. I found a reasonably priced double-ended one that seems suitable:

MH-DE400/TD/4K (400w, double-ended, 4200k, 36000 lumens, $49.95
at http://www.bulbsource.com/MHDoubleEnded.htm

I don't know if HQI is something different, though. If anyone knows of some bulbs that would work with this ballast, or the socket required, that would be of great help. Thanks!

Here's a picture of the ballast.

Ok, so HQI is just double-ended. I hate to double post, but could someone tell me if an HQI electronic ballast, as in this one, could run a non-HQI bulb? As in mogul socket, like an EYE?

I would just go with the HQI bulb. Try to find the best color temp and lumen output and go for it. The HQI is a great way to go but they tend to be more expensive, which, I believe, is the reason that they are not in the Lumenlab plan.