It's rare to find any iPad case for $20, and even less common to find one that includes both a shell and a lid. But that's just what you get with Macally's Clear Case with Reversible Cover for iPad Air ($20, aka CMATEPA5): the case is composed of of a clear plastic shell that snaps on to the back of the tablet, and a detachable three-columned lid. One of the lid's sides is microfiber, the other is a different synthetic fabric. Instead of magnetically…