I would definitely stay with CFLs instead of going with an HPS in your space. That would pose even more heat issues to tackle, imo.
Problem with the heat buildup is due to the PC fans; they don't have enough CFMs to move/replace the air in such a significantly large space effectively. So, as soon as they move the air, the CFLs are perpetually creating more heat than they can replace, while hotspots are also a factor. If you could create a simple CFL fixture to mount your lights to (check out some of the cool DIYs on RIU), then cut/saw square openings to mount your PC fans above the lights.....this will allow the fans to suck/pull the hot air from the CFLs and out of the fixture. You can mount ducting on each fan, leading out of your cab to help redirect the hot air.
Since your ambient temps are not too bad at 80°, you will be golden once you get the CFL heat contained. They shouldn't increase the temps in your cab by no more than 2-5° if done properly. So your max temps would be about 85, which isn't bad, as long as the heat from your bulbs are effectively blowing away from your plants and out of your cab. Oh yeah, and make sure your intake ventilation is allowing enough air to come into your cab, otherwise the hot, stale air surrounds your plants leaves. And your leaves will actually be MUCH hotter than the temps in the air surrounding them.
I had the same issues with my growbuckets, so I'm here to help!