Mine was indeed $18 but that was skin only (no batt/charger) and on clearance, they're around $90 normally. Makita do make a 36V version that takes 2x18v batteries, at around $350 (brushless motor too from memory), I was going to get one but now I think it might just be awkward. The 18V is only about 2' long so super easy to direct where you want it.
The Ryobi looks OK but the length and kicked up air exit may not be ideal in this case, though I suppose you can use it without the nose extension, once you protect the edges so they don't scratch.
For hard water, you can also get one of these:
http://www.wolfgangcarcare.com/deluxefilter.html
I tried it out today on my Golf, after a mitt wash with Gyeon Bathe+ (adds a very light coating). Also, the roof was already coated and the windows have Rain-X.
The Ryobi was easy to manipulate and the battery lasted the whole 20 minutes (a Mk7 Golf is 'only' a hatchback but quite a bit bigger than a 500). I didn't use the flicked-up end accessory on the pipe. The '250km/h' airflow didn't seem too amazing after all, I suspect volume is more important than speed!
Yes, it took me 20 minutes to dry the whole car... the roof, windscreen, and bonnet were by far the most annoying, as little balls of water were chased everywhere. The sides, windows, window rubbers, mirrors, and front/rear grilles were very easy to dry, as were the wheels. Some of these areas are difficult to dry with a microfibre towel and it was particularly satisfying to eliminate the usual dribbles of water from around the tailgate and mirrors which a towel never quite gets.
Therefore, I think I will refine the technique by using the microfibre towel to dry the large areas (roof, bonnet, windscreen), perhaps using quick detailing spray if the car has only been snow foamed and not mitted. Then I will use the blower to dry everything else.
I also wonder whether I sprayed down the car with the wrong spray pattern from the hose gun - if the coating does what it's supposed to, then most of the water is supposed to sheet off the surface. I just had a million tiny beads to chase around
Suspect that if I'd used a jet, then less water would have remained.
In summary I'm very glad to have this new technique - it does a fine job of blowing out the annoying tiny leaves and petals that descend into my window rubbers etc. even in the few minutes after washing (I have to wash in the shade under a tree), the wheels look great, and I can't stress enough how good it is not to have those dribbles from around the tailgate etc.
The water filter is a good idea and I will look out for that. Thanks again.
-Alex