A nice used .22lr revolver like a Ruger Bearcat or a Single Six would be great for a kid because of the simplicity and ease of operation. I have seen many used Single Six revolver in great shape for well less than $400 and some for less than $300. Another option if on a limited budget would be a Heritage Arms Rough Rider. Not as well made as a Ruger or a Smith but very serviceable. My brother has one, a .22lr/.22mag convertible and it goes bang every time and pretty accurate. Not bad for less than $200 for the .22lr and a bit more than $250 for the convertible.
If you must have a semi-auto then I concur with those who suggested the Ruger Mark III or 22/45. Both of these can be had for well less than $400 on sale. A Smith and Wesson 22a are on sale for less than $300 and they are an accurate handgun.
If you must have a semi-auto then I concur with those who suggested the Ruger Mark III or 22/45. Both of these can be had for well less than $400 on sale. A Smith and Wesson 22a are on sale for less than $300 and they are an accurate handgun.