I've done some research, now I'm seeking experienced consultations /
opinions.

My current growroom is 54" long, 30" deep, and 68" tall for a total of 76.5
cubic feet. I have an exhaust fan rated at 70cfm installed in the ceiling
and an air intake at ground level.

I'm currently lighting with a dozen cfls at mixed wattages from 27-42 watts
each and seem to be doing pretty well. It's just irritating having to raise
the lights on a daily basis to keep the leaves from grabbing hold of 'em.

I want to switch to a mh/hps system and found a 400 watt switchable
system here: Grow Light Kit- 400W HPS MH Digital Ballast, Full Spectrum Bulb, Reflector

(sorry if the link stretches the screen)

My current temps in the room stay at around 76degrees f at plant level,
and never rises more than a degree or two max recorded temp.
Humidity stays at 30-40.

Will this be the way to go or am I aiming low to keep my lighting system
under US$200.00?

Will I need additional cooling? I know I've got about 8 or 10 degrees to
play with before I've gone over the maximum recommended temp.

Thanks in advance guys.

oh, btw, my ballast will be in the grow room mounted near the exhaust fan.

Anybody think a 400watt mh/hps in my current setup be too hot?

Go to htgsupply.com, if you want a ballast and bulb cheap. I got mine for a $130