I got mine at Buckeye Hydro. One of their people, Russ, posts here. He was tremendously helpful in getting me exactly what I needed, including things like a connection to a garden hose spigot, things like that.
Ultimately you get what you pay for. Buckeye Hydro isn't necessarily the cheapest but the service was perfect, and to me service is worth a lot. In the end, IMO, I got more than I paid for.
I paid something near $150 for my system, IIRC, plus I added a TDS (Total Dissolved Solids) meter. I think the latter is absolutely necessary, as I need to know when the system is no longer working optimally. I'd hate to keep producing RO water only to find out, later, that it had stated to produce 100ppm or greater water when I was counting on 5ppm.
A few tidbits I picked up along the way:
1. Feeding softened water to the RO filter works better than unsoftened water. My local water is really bad in terms of alkalinity, so it's softened.
2. RO systems work slower if the water is really cold. When I get to the spring when water coming in from our underground pipes is cold, it slows down. In August and September, it's pretty fast.
3. I selected the 50 gpd (gallons per day) model; It will produce about 2 gallons per hour but that's under optimal conditions (warmer water). During cold periods it's about 1.5 or so. In retrospect I kind of wish I'd chosen the 75 gpd system. I can replace the 50gpd filter with a 75gpd filter if I want to, but the system continues to work fine, so no need.
4. I always flush the system for 30 seconds before beginning, and for 30 seconds when I'm finished. It always takes a few minutes for the water coming out of the system to drop down to the 5-6ppm level it always settles at. So at the beginning I'll let it run for maybe 5 minutes after flushing, then direct the output into a small cup in which I've placed the TDS meter. That way I'm sure the system is performing, and at that point, I'll put the output line into the Aquatainer I use.
5. My standard procedure is to pump the RO water into my kettle at the start of brew day, then set the RO system to refilling the Aquatainer while I brew. That way I always have enough RO water to do the next brew day. Occasionally as I use up my 1-gallon jugs of RO water I'll refill them from the Aquatainer and then set to refilling that.
6. I've had two back surgeries. My Aquatainer is 7 gallons, and it dawned on me that even though I can lift that to a table on which I can fill pitchers to transfer water to my kettle, or fill the 1-gallon jugs, I might be tempting fate. So I researched and bought a transfer pump that I use to get water from the Aquatainer on the floor to the kettles, or to the jugs. I've shown how I do that below in a couple pics, and here's the source of that pump:
Power Supply:
https://www.amazon.com/gp/product/B073QTNF9F/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Pump:
https://www.amazon.com/gp/product/B07FT87XJY/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1