I have the CR Spotless De-ionizing Water System (model # DI-120) it works as advertised. Use as a last rinse and walk away, dries spot free. That particular model is a bit cheaper than the rest, I think it was like $250, and the replacement packs are like $40. It's supposed to get 100 of gallons of water before you need to replace the resin. And the nozzle runs at 2 gal/minute so if you use it for like 2-3 minutes as a last rinse, you're using about 4-6 gallons which implies you should get 20 or more washes out of it (for $40 per replacement pack, so $2 to NOT have to dry your car). I heard you can get them cheaper on amazon or something, I haven't needed on yet.
The next model up is $300 and gets 150 gallons, so that price works out better cost/gallon. (replacement pack is still $40)
I wait until it's dry and still pass with a spray detailer or spray sealant (Hybrid V-7).
Before I bought the system I would go to walmart and buy gallons of distilled water for 80 cents each, use about 3 or 4 at the end of the rinse... works just the same. Sometimes I even dipped the waffle weave drying towel in it and wring it out real good to dry the car like that, give it a quick wipe and any "streaks" left behind are distilled water so it evaporates away perfectly.