I would imagine that the ATC spindle would cost more than the non-ATC variant, but these things are around 6-10 times the cost of the non-ATC (the er11 collet) spindles. Note that I'm comparing the k-l2200 to the kl-2200ATC and the same deal with the kl-4500 I'm assuming they have the same motor and same if not very similar bearings (could be wrong on that). I would imagine they have some pneumatic mechanism to grab the tool holder, consisting of a solenoid, a piston and some moving parts. I am just very surprised at how much more you have to pay to get a spindle compatible with an automatic tool changer... its not like the spindle comes in a package with a complete ATC system.
I believe the huge price difference is not that the ATC spindles are very expensive, but because of how cheap the standard spindles are. I've seen 2.2Kw spindles as low as $250.
Compare a non ATC chinese spindle vs a similar power HSD. The chinese spindle is 5-10 times cheaper. This is most likely due to the huge volumes of these being produced. There are numerous sellers on Ebay, from what appears to be many different manufacturers. I'd imagine that ATC spindles are produced in much smaller quantities. In the 5 years or so that the chinese spindles have been available, I've seen one person purchase an ATC spindle, while hundreds have purchased the standard chinese spindles.
If you look at a standard and ATC spindle from a manufacturer like HSD, you'll see that the ATC sindle is 2-3 times more expensive.
A chinese ATC spindle is probably 30%-60% cheaper than an HSD or Colombo ATC spindle.
Mach3 2010 Screenset
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)