You need to specify how big of a chiller you need because that matters
; I guess people can search through your posts and find out how big your tank is; assuming you posted that somewhere here or there;
I have three systems currently:
100 Gallon corner tank (basically an all-in-one, acrylic) <- the one that started it all, bought for $50... a few thousand dollars later and I'm a reefer. It's not in it's prime. (it's been better) Lighting and chemistry have been my main issues here.
55 Gallon. This was a free tank and has mostly been created off of free (or cheap) items. It was an experiment in rock only filtration at first (minimalist approach). Literally was just 1/2 full of water and a ton of live rock and a powerhead. Ran many months like this and was great. No real coral to speak of until recently, when I got a lot of free livestock. I added fish gradually and just last night completed an overflow (hang on syphon type, tank is not drilled) to sump to hang-on-back refuge. (The return pump of the sump goes into the input of the refuge!) The flow of this part is slow, hoping to add another overflow later but there is a powerhead and I stuck an internal submersible filter into the main tank as well. I just picked up a great combo light (t5, MH, LED) for this but with this heat, I'm afraid to run it!
and a "frag" tank, this is the start of my "tri-level" system. So far it consists of a 2x2 frag tank over a 90 gal sump. (the sump actually has most of the wildlife!) There is another 2x2 frag tank on that second shelf but it's self contained and only has a few mangroves and algae in it so I'm not concerned about that portion at all.
I have thought to combine the contents of the 55 and the "frag" system into a bigger tank (I just picked up that 180 stand, after all!) The overall cost of doing that would probably be less than trying to buy multiple chillers and would probably result in a more stable system as well. Heck, I might put everything together into that and give away the excesses.
But that will take some time and it'll be cooler by then.