The most important aspect in our business is designing and building our environments. Before trying to find a good deal on an AC, know exactly what you will need from A to Z.
First calculate how many BTU's you will need, which I recommend 6,000 btu's per 1,000 watt light.
Then determine which style of AC you will buy. Portable, Window, Mini Split, and Central AC Split System are your options.
They all have pros and cons, but once you select which type you need, then search for deals with the BTU required. Don't search for deals first.
For 1-2 lights, you can use a portable with dual hose (1 for intake and 1 for exhaust)
3-6 lights you should use a mini split
6-12 lights you should use either 2 mini splits or a Central AC Split System.
If you are on a budget and location permits, you can use window AC's, which are very cost effective.
Just make sure you get an AC that doesn't blow the room air to the outside for CO2 and Odor control purposes.