a used S&W m17 (k22) or M18 are great revolvers
This!
First, I admit I am very biased in favor of the S&W K-22 models.
Second though, your budget is $600, correct?
The out of production K-22s are among the finest .22LR caliber handguns, revolver or auto, ever created. They used to be much more common, but people are finding out for themselves how great these guns really are, and they are being snatched up in quick fashion.
And the prices are climbing pretty rapidly, though you should be able to find one within or a little under your budget. But I fear they won't be that way for long. At the current rate of price escalation, a typically S&W Model 17 or Model 18 K-22 will be fetching north of $750 a few years from now. The Colt Diamondback in .22 LR is a good example of this; I've never actually seen one, and I believe that when they do turn up they fetch north of a grand.
As long as the Ruger Mark and Six Series, Browning Buckmarks, S&W 22As, Berretta Neos etc are still in production, their prices will be stable. In other words, you can pick one up at any time. But their are only so many older K-22 Model 17s and 18s to go around, and people are tending to hold onto them once they acquire them.
The K-22 line adopted S&W's now familiar model numbering sequence in 1957. These guns are built on the ubiquitous and highly successful S&W K Frame, which includes such guns as the .38 Special S&W Model 10 and .357 Magnum Models 19 and 66, just to name a few. The S&W Model 18 / K-22 Combat Masterpiece was only offered with a 4" barrel. The Model 17 / K-22 Masterpiece was most commonly offerred with a 6" barrel, but others were sold with 8 3/8" tubes and more recent guns (from '86 onwards) were also offered with a 4" barrel, once the Model 18 was discontinued. Both were sold with a blued finish, though there are some VERY rare factory nickle finish models floating around. The 6" Model 17 / K-22 is the most common of the K-22s, and is therefore generally the most affordable. 4" Model 18s generally command a $100 or more premium.
I own a M17-0 (made in 1959) and it is a joy to shoot. I bought it more than 2 years ago for $430. This same gun would probably sell for $550 today. Perhaps even higher, as I do have the original Diamond Magna wood stocks for it (first two pictures). These stocks can fetch $200+ all on their own. These guns are finely crafted, with excellent workmanship. They are exceptionally accurate, and with care, they should last several lifetimes, especially when considering the fact that the K-Frame on which they were based is also used for .357 Magnum handguns.
Still, at $550 it would be a great bargain, when you think about it. For me, it is nicer than it's successor, the stainless steel S&W 617, since the 17/18's no lug barrel balances better in my hands. And even at $550, it still costs less than a NIB 617. And though S&W is now producting the Model 17 "Classic" again (as of just recently), they are even pricier than the NIB 617s.
My K-22 nearly always comes to the range with me, and it is always a big hit with everyone who tries it, from novices to old pros alike.