Hi and welcome!
As with all of reefing, there are varied opinions. Personally, I don't think a chiller is worth it. I keep my reef at 80-82ish with 3 250W MH over it. I use 2 4" fans mounted in the canopy, and they do an amazing job of managing the temperature. Granted, you've got a lot of light there (what are you planning to keep?), but you might be able to spare the expense with fans. By this, I mean the energy expense - those chillers are energy burners.
When we first got into the hobby, we thought we'd need one too. Once we learned a little more about where our temps would be, and how we could manage it, we decided to pass on it. Just something to think about...
But then again, you've got a whole lot of MH going on...
Does your electric company send you a Christmas/Thank You card?

I should hope so! (Or maybe you've converted to wind power or solar?

)
Good luck, and sorry to not be much help in the chiller department.
Danielle