I paid $409.00 for one new in box that I ordered from Smith through a local dealer 2 1/2 years ago. 6" 10 shot, steel cylinder.
2 months, and a few hundred rounds later, I traded it on a Browning HP Practical and recieved $325.00 credit towards the HP, and was happy to be rid of troublesome 617.
FWIW, I went on to buy 2 older Model 17's for $350.00 each and couldn't be happier.
My 617 was horrible. Bore so rough it was impossible to shoot more than a few rounds before it would keyhole. Inaccurate. Light hammer strikes caused frequent misfires--getting through 1 10 round cylinder w/out a misfire was rare. Terrible rough creepy trigger.
All of the aforementioned could have been solved by sending it back to Smith since it was under warranty. The main reason I didn't like it though was the 10 shot cylinder and the round butt frame,,,,neither of which could be undone. I wanted a direct replacement, in .22 for my 6 shot Model 19-4 so that I could shoot cheap. I looked and looked for a nice older Model 17 for a couple of years before I gave up and settled with the new 617.
As luck would have it, I stumbled onto not 1, but 2 very nice 17's a year and a half later.
Based on what I paid new for mine, and what the dealer offered me on a trade for what was essentailly a 99% gun, I'd say $350 would be a fair price. That assumes of course that the one you have in mind has a steel cylinder. If the cylinder is aluminum,,,,$50.00 might be a generous offer.