I just put together my own from ebay. You need a 1/4" line to feed a sediment filter, with a post-carbon filter to follow it between the Sediment and RO membrane.
I put a 100/gal a day RO filter together from components for about $50.
Geek pure makes a good 75gal/day countertop setup for about $60 you can get it on Amazon. You'll get about 6 months from a membrane about 3-4 from the carbon and about a year out of the Sediment filter. Longer if just Ro filtering tap water.
P s. I grew DWC for years and years. Tap water works just fine and actually takes away the need for so much cal-mag and silica in most municipalities if you can come up with a way to make it work. And that applies to pretty much all hydro methods. Tap water is actually your friend and the light chlorine helps keep the buckets sterile for longer if your temps aren't super stable (although that was more of a problem back in the hps days)
Seedlings will usually do fine anywhere from 0-120ish ppm and ph anywhere from 5.5 to 7.5, some can take even higher for the first early stretch in Dwc. You don't have to number chase much until those cotyledons start to fade. And you can start feeding light when that happens anyway. If your up high though you have to correct immediately upon first signs of coty fade tho.
When in Dwc I would start seeds in peat pellets with un Ph'd tap or bottled water. And transfer them to the pellets/buckets at first signs of coty fade. And then start worrying about number hunting, ph, ppm/ec, and nutrient levels.