I think you'll be lucky to find £/€600 in good condition these days. I mean I thought I was lucky 3 years ago and pounced on it.. But 800-900 is definitely doable. Even though the ones on now seem to be asking more like £1000.Price of the JS1000? TOO CHEAP is what it is haha.
Best value prospect of basically any guitar on the planet. But in general, your analysis is correct; they are all over the place, but typically they are dirt cheap. Just pay attention to the overall state of the guitar, seeing one for 600 pounds isnt a "too good to be true" price for them. A "good deal" for me would be anything under 800$ in decent shape. 1000$ is pretty much normal for them.