Where can i get a good but cheap microscope for my son?

my 12 year old son is really getting into science. And ever since he did a lab experiment in school using microscopes he really got into it. And now he's keeps asking me for microscope. And i would really want to buy one for him but there really expensive. I would want one that is around one hundred. but not a cheap one that magnifies only 5 to 10x's