How fussy are you about your trigger? How much tinkering with the guns do you mind doing or paying to have done to achieve the sort of trigger you like? The guns that $300 will buy are not going to be bottom feeders but they won't be far from it. And they will all be the guns that folks buy only to sell later when they "upgrade" to a S&W, Dan Wesson, Colt or Ruger. The reason those four names keep coming up and why they command the used prices they do is because the guns are truly superb to shoot thanks to their excellent trigger designs. And they will last for many hundreds of thousands of rounds without even breathing hard. This makes them good value despite the higher purchase price.
I don't admit to having tried a huge number of .22 revolvers but I quickly came to the conclusion that paying more to get the best was money well spent. I got an H&R Sportsman and shortly after a Hi Standard Double 9. Both not bad guns at all. But niether could hold a candle to the S&W Model 17 that I got when I came across a bit of a deal from a buddy. A year and a bit later I found an older mid 60's Ruger Single Six three screw that was tight but worn a bit for $150 and the debit card hit the counter again in a blink.
Despite some tinkering to make it better the Double 9 went to a buddy. It would have taken a LOT more tinkering than what I did to make the trigger on it match the Ruger. And with the design of the double action system there was just no way to make the double action pull in any way become tolerable for target shooting or even basic pop can plinking. The H&R is still with me and I'm going to continue to tinker with it because it's the top break model and I like it for this particular feature. But it can't hold a candle to the S&W 17 for double action feel although the single action trigger is already very nice. And again due to the nature of the double action system in the H&R I doubt it'll ever become near as nice as the Snith.
I've seen lots of mixed reviews of Taurus 94's. If you're lucky to get a good one or don't mind the trip or two back for warranty and then tinker the trigger to get the feel you want they seem to be good after that and last a long time. But it seems like a higher percentage than normal need to go back for one thing or another and from reviews that the trigger out of the box can't match the S&W (or Colt .22 if you can find one for a decent price). Given that there's this gamble for getting the trigger to feel like you may want it may or many not come out the other side of the work costing less than a nice used S&W.
I can't comment on the Charter arms models as I've never had a chance to shoot one or even read many reviews of them since they are rarely sold up this way.
I may be in for a lot more tinkering to get what I want but I'm likely going to throw the debit card down again for the new Ruger SP101 8 shot .22 when it comes out.
Anyhow, the moral of this "story" is to see if you can try a few of the guns first. In the case of the S&W 17 or 617 you may not be able to try one of them but if you can get to shoot one of the .38spl K frame guns then it'll feel pretty much the same but with less kick
At least dry fire a K frame gun so you know what the trigger will feel like to compare to the other options.
If you're looking for a single action plinker the one option I'd suggest despite being untried is the H&R 9 shot models where you pull the cylinder arbor pin out each time to drop the cylinder and load it externally. It may seem cumbersome at first but as long as you've got a range table and a mat to do this it's actually quicker than single unloading and loading with a typical single action gun such as the Ruger Single Six. And if you can make up a block of wood with 9 brass rods in it to eject all the empties at one stroke it becomes very quick. You just need to shoot in situations where you can have the loose parts laying around. So it's not that good for field plinking. For such use you're better off with a regular single action type or a break top or a swing out cylinder.