sniper,
It really would be nice to know what state you are from. This could help us give you a better answer to your question.
In my situation, I have a 375 gallon tank that is in the wall (one side is where the basement is and the other side is the garage where the majority of the tank, stand and all equipment resides).
I have an attic fan rated for 2500 sq ft one the opposite wall to the crawl space. I also have a vent on the crawl space. When the internal temp to the garage reaches 75 degrees, the attic fan automatically turns on blowing all the hot air out of the garage and sucks in all the cool air from the crawl space. My garage is the coolest place in the house. Last year here in WA, we had 97 degree weather for several days, my tank temp only rose 1-2 degrees to 80.6. My house does not have A/C.
To date <knock on the proverbial wood>, I do not use a chiller.
I kept an Excel spreadsheet and would log my temperature daily. I would take it the same time every day. Once when I woke up and another right before I went to bed. I did this for one month before any fish entered the tank. The only source of cooling was a clip on fan that blew across the entire tank.
So placement of the tank as well as local climate play major roles on whether you need a chiller or not.
HTH,
Kirk