I bought an unfired blue 6" Python w/ box, no papers last year for $700 and was happy w/ purchase, although I haven't shot it yet, probably won't. If I could find a 4" as you've described for $700 I would buy it, use it, & enjoy it. Sounds very fair to me.
I bought one as you described a couple of months ago for $500 (but that is why I bought it!). I would lay $600 cash on the table and have a couple of fifty's handy in case you have to up the ante. Probably worth the $700 if that is what you are looking for.
A friend of mine recently bought a 6" nickle one for $750 and thought it was a good price based on some price research he had done. It hadn't been shot hardly any and the original checkered grips look like new!