Before you spend more money on a chiller, I would recommend several things:
1. figure out what lights you are going with. If l.e.d my assumption is no. I had 6 x 80watt t-5's with a small fan over my 220 and the most I ever did was put a 2 liter pop bottle of ice in the sump, periodically just to cool it a little more. If you are doing mh then I'm sure a chiller would be needed
2. Set up your tank, get it cycling and see where the temperature lands. At least that way you can determine how much of an issue cooling will be.
Just my 2 cents