The RO/DI units from
www.bulkreefsupply.com are usually well-priced. I've found the units designed for home use to be much more expensive than the ones for aquarium use (which is really weird). Plus, if you buy a home RO you will probably have to add the DI chamber anyway. What is the TDS out of your tap? If you don't know, go buy a handheld digital TDS meter. They cost about $15-30+ depending on brand for a real basic one. That will do the trick. Knowing the TDS (total dissolved solids) is really important when choosing an RO/DI unit. Are you on well water or city water?
If I were you I would avoid a chiller at all costs. They are expensive to buy and expensive to run. They also add a significant amount of heat to the room they are operating in. Unless you can plumb it to run outside, I would strongly suggest you look into other options. Like designing a canopy with airflow, adding fans, etc. Jebo (a cheap brand) puts out very cheap fans. I like cheap fans because they get all gummed up with salt creep and rusted, and only last a couple years at most I find, so cheap fans are good! The Jebo fans come single or in a bank of up to 4 fans. They move plenty of air, and don't suck up a bunch of electricity. They can be taken apart and washed too. I have two 3 fan Jebos on my tank...one on the rim of the display blowing the hot halide air out, and one in the sump blowing cool air towards the sump water. This keeps the temperature at 80 in the hot summer. Central air conditioning keeps the room around 78 (I'm cheap on a/c). There are two 250 watt halides on my tank. A floor fan 10' away from the tank will help blow cooler air towards the tank as well as move air in the house.
I would spend $3000 on central air conditioning before I bought a chiller. Even a window a/c unit near the tank will do the trick.