Lots of threads on here about this. Somewhere out there in the vastnest of intracoastal America, the LGSs may be teeming with pristine 17s and 18s for $600, but here on the East Coast it's been years since I've seen one. I hunted for several years before finding a 4" K-22 at all; wound up paying $725 for a 95% pre-18 a year ago. Since then, I've seen a few at the big Nation's Gun Show in Chantilly for $800 and up.
17s are somewhat more common and somewhat less.
As always, check the completed sales on Gunbroker for an idea of national prices.