A good (and inexpensive) images manager for Mac?
Well, you could try some sort of "anything bucket" like DevonThink or Yojimbo, as those should be pretty capable of handling the search and metadata parts, but I think those might be tad bit overkill if you only want to use it for images.

I am not sure how powerful the image managing part is, as I mostly use the conversion and editing tools, but GraphicConverter has some image managing parts built into it and might be worth a try:

http://www.lemkesoft.com/content/188/graphicconverter.html

As I said, it mostly is a conversion and light editing tool, but since it is an old-school shareware program, you can try it out for free to see if it suits your taste. In that case, I would recommend trying out both version 6 and 7, as 7 was a complete rewrite and as far as I know has not yet full feature parity with the older version.