Except for the lens salvaged from a smartphone, the Lego Microscope is built entirely out of Lego bricks. All of the instructions for creating your own are available in several different languages. The scientists had success with their creation with students age 9-13.
The article also mentions the foldscope. Science teachers probably already know about it, but I was this days old when I learned about it. The foldscope is a paper microscope with magnets that can be made for less than $1 yet be able to resolve single-celled organisms.
Very cool stuff for science teachers!!