There are low-cost options too:

I had fun years ago using the lens from a CD player laser as a microscope for my phone. The setup is dead simple: hold the lens with a bobby pin and attach it in front of your phone's camera with a rubber band. A portable microscope that records video!

There are also small plastic scopes about the size of a D battery (would recommend one with lights). Definitely toys, but uh toys can be fun too.