Just a" Ball Park" guess more than anything else....
..That'd definitely be a "Square Butt". Pricing is really hard as the model 66 has been eclipsed by the 686. Which is a heavier frame, and thus better suited to continual use with 357 Magnum rounds. The "K" Frame, which is what the 66 is, was intended for the 38 Special more than 357 Magnum. .... So, the market, as with most things rules; if a buyer really wants it, then obviously price is not much of an issue. All that being said, you might want to do a little Internet Search, or your local Library/Gun Store on used Gun prices. Most being listed for US prices and market.......... At a guess, I'd think, between $550 and $650, but it would be interesting to see what offers you'd get for it............ Personally, I really always liked the Model 19 and it's later reincarnation, the model 66. Great with 38 Spl.! Easy to tune and polish, very accurate and relaible ! ..... David K