The prices are pretty similar to Yamaha DX series synths on eBay right now (starting at about $300 and going on up to $700 for working specimens, depending on model and condition).
replyNot really. XZ1000 $300-600. DX7 $700-1000.
replyAccording to what I can dig up, the original MSRP of the DX7 was $1995. The original MSRP of the Casio CZ 101 was $395. So, by my reckoning, the CZ has a higher collector value than the DX7 based on relative price change over the years.
replyEdit: But also, the CZ was generally more comparable to lower-end DX synths, like the DX27 or DX9. It was a budget synth in its day, while the DX7 was the pinnacle of digital synthesis for at least a year or two after release, everyone had to have one.
The core of the vintage remake market is "Always wanted this, still can only afford a clone" which is where Behringer lives.
replyThere's also a "Always wanted this, can finally afford it now that I'm rich" niche for the high-end remakes from Korg and occasionally Moog etc.
There isn't a huge "Bought this forty years ago because I couldn't afford anything better and would quite like a modern remake" segment.
Casio do still make pianos and Casiotone keys which include samples and some CZ and VZ series sounds. (I don't know if they're sampled or DSP.)