Ok - I just went and used Gunbroker's advanced search feature to hunt up closed/completed/sold auctions on 4" 686's. Over the past 2 months, they've pretty much run $475 to $650, with the higher range being older guns in good shape with original wood target grips and/or original boxes. I consider as a rule, when buying from Gunbroker to assume a $50 federal "tax" as that is what it usually runs above the gavel price to get it through federally dictated shipping requirements and a local FFL transfer before it gets into your hands. Thus, those people paying $650 are really paying about $700. Gasp.
So you are right, these things are really pulling down the cash they were not 12 months and 24 months ago. Maybe it's because I post so frequently about what wonderful guns the 4" 686's are
. But now I had a like-new (mint) 686-4 2.5" in the original box, with wood grips, for sale on the classifieds here and elsewhere this spring, and it took a while to sell at $600. And 2.5" guns in the box usually bring a good premium over a 4".
All that said, my strategy would be to find a pre-lock/pre-MIM (eg., 1997 or earlier) 686 with the original box or at least original wood grips and try to pay $550 before shipping and tax. then I might be $600 all in, but I would have a desirable one that will always bring a premium over newer models.
Last word is that I would not be in a hurry - I see plenty of signs the market is curbing and a peak was hit and prices are dropping. People are just tapped out from gorging on guns and ammo the last year. I offered up an excellent 66-1 2.5" .357 recently at a price that would have moved quickly six months ago; I've had barely an inquiry. This is not my only data point, but it's a valid comparison point. I'd buy later in the summer and take my time about it.
