Anybody have experience with one?
I have the original...just like the one in the eBay link above.
I used it for awhile a long time ago...back in the early 90's...and I have to say, it is capable of some nice amp simulations. I actually like it better than some of the digital fodder out there these days as I just can't get past the digital "sound" which I can hear when I'm actually playing through it in my room...though in a mix, I guess it can be masked fairly well. But the SansAmp has that analog vibe.
Anyway...not sure what is a "good" price for a used one, but I don't think you will be disappointed with the overall sound quality and its ability to cover a lot of amp tones.
Biggest PITA are the small dip switches. You need a narrow tool, (I guess a small screwdriver works, just don't break the one of the dips

)...
...other than that, I never had any issues/complaints about it.
I use to use it together with a H&K Red Box...that way I go amp and cab simulation, and was able to run the balanced XLR outout of the H&K right into mixer's balanced mic inputs.
Heck...I may break mine out this weekend and give it whirl...it's just been sitting there, since I use real amps these days and have a few decent ones to pick from...but I bet I could coax some nice tones out of it that would fit alongside my real amps.