you can buy sealed warehouse lamp units second hand on ebay.
they are solid steel (and i mean solid) with ballasts built in they do not emit as much heat as a bare bulb or a cheap crap chinese reflector unit that you pay through the nose for because it is labelled hydroponic.
they are called low bay warehouse lights and they are fitted horizontally, they have to be solid and have safety glass fitted as health and safety is paramount in the workplace. ( metal halide bulbs have been known to explode )
they are usually metal halide but you can rip out the guts and just feed in your own ballast cable and reconnect it to the lamp holder and then put it back together and add your 600w hps.
you can also get hps ones.
heres one that requires a piece of glass added.
http://www.ebay.co.uk/itm/Fitzgerald-low-bay-Light-fitting-/190703344876?pt=UK_BOI_Lights_Lighting_ET&hash=item2c66ce1cec
i bet you a million bucks you get down to about 20-25c temps.
i got 10 used ones on ebay uk for £150 second hand 2 years ago. ($233.15)