There are a few very good choices for under $300. The cheapest, if found on sale, is the S&W 22A mentioned above. These are exceptionally accurate and reliable, as much as more expensive .22 semi's. Trigger is on par with the MKIII. They also field-strip in about eight seconds. Be aware that they also have the largest grip diameter, so not good for small hands. These provide the most bang for the buck.
The Beretta Neos is also in your price range. Their triggers aren't as good as the Ruger and 22A, but they are fairly accurate. These have the smallest grip of this group, so good for smaller hands. Almost as easy to strip as the 22A. It's my least favorite .22lr in our collection.
The Ruger MKIII's are excellent, but the only one you will be able to get in your price range is the one with the regular barrel and fixed sights. These are not easy to strip, but they are built better than anything else in this price range. Triggers are good -- not as good as the BM -- but a lot better than the Neos. The polymer 22/45's are in your price range, but they are not as nice as the MK's.
The basic Browning Buckmark can be found in your price range too. These have the nicest trigger in this group, and have a pleasing grip shape that fits most people. Downsides are minor - they need a tool to strip, and they only come with one magazine. This is my favorite low-end .22lr semi-auto, and is the one I would own if I could only have one.
