fwiw, I have your problem (all year), and low water pressure to boot. I had to bite the bullet about 5 years ago and bought a Kold-Steril unit. RO was just a nightmare for me. 12 gallons waste to 1 gallon product November through April. At its' best I got it down to 6:1 in summer. Though I pay almost nothing for water, I do have a septic system, so I just couldn't put all that water down there. I was very fortunate in that my source water is very low in phosphates, but silicates are a little high. It worked perfectly for me. Maybe too perfect. I evaporate almost 5 gallons a day with all the sw in my basement now. RO water would be nice, but in my case not a necessity. Poly-Bio-Marine is a real PITA to deal with, since their filters occasionally go AWOL in the market for months, but they are cheaper and easier to deal with that RO, imho.
If your needs aren't too great, mxing your incoming water line to get the right incoming temp. may be your best solution.
I think one of the RC sponsors designed a cold-water RO system, though I can't remember which.