Hey MJMP,
I was just looking at a D640, and I realized, that the .64i is the same thing, just a newer model with a few more bells and whistles. I think the "i" series delays just replaced the older versions.
On average, I paid $90-$100 for each of the S-1000's, "i' series, and Digitizer's. I may have paid about that much for the Pitchtraq's I have as well, and I never paid more than $120 for the Microcab II's I have.
I think the Ampulators are going for those high prices because there weren't that many made. But $1000-$2000 for a STD-1??? I'd rather spend that kind of money on a used TC Electronics 2290! At least with that you get all the same delays and more, plus it's frequency response is 20,000Khz with a high frequency roll-off at 20,000-30,000Khz.
I know the human ear can't hear anything above 20,000KHz, but the brain can sense it! That gets into some pretty heavy aural science
Harley