pros and cons of .22 semi-autos vs revolvers...
to me it comes down to ammo / and many .22 semi-autos will not run on cheap bulk .22 ammo without a lot of FTF's or misfires ( like the Remington bulk paks). Most of the mfg's will recommend you run a premium .22 round like CCI Mini-Mag and its about $ 10 - $ 12 for a box of 100 rds.
.22 revolvers ...of course will run anything that you can fit into the cyclinder..
A longer sight plane on a gun ...for plinking...makes it a little easier to shoot it more accurately...so the revolver shines here too. S&W makes a great revolver - but you said its out of your price range...maybe if you to a used gun, you can find something....but, yes, they are not cheap - but you do get what you pay for sometimes...
If I had to pick one semi-auto .22 ...it would be the Browning Buckmark. Even the least expensive model, the camper, is a nice gun ...and they tend to run pretty well, even on bulk ammo. Another gun, that I see at a lot of gun shows is the old High Standard semi-auto ...and I'm seeing a lot of them for under $ 400 ...and in great shape. They have spectacular triggers...and they are incredibly accurate..( a little ugly ) ...but I can get past that...
Its not a clear - go revolver or go semi-auto to me....so I have more than one of both ....( S&W revolvers mod 617's, model 18's / a Buckmark, an old high standard, some 1911 conversion kits...a sig 226 conversion kit...) ...