I bought one of these around 15 years ago from Costco at the time. It's well worth it for me. I use as a final rinse, no water spots. The resin lasts me a good year doing regular washings on 3-4 vehicles. They even have a resin exchange program where they send you tubes with new resin and you put your old ones in a box and return (shipping label provided).
Spotless Water Deionization Systems - Wash, rinse and go! CR Spotless Water Systems are portable de-ionization
crspotless.com
Edit - just got an email from them on Black Friday Sale now on: 15% off
Use Code: BLACKFRIDAY