After a brief search I found this stereo microscope and this compound microscope which should be good enough. heck, here's a popular cheap one as well. It comes with a bunch of unneccessary stuff but it should be good enough.
If all you want to do is look at some tardigrades for a while then I'd recommend the cheap one. All you'll need is 10x to 50x zoom.
If you're wanting this to be more of a hobby then it'd make more sense to invest more into it. If you're really serious I'd recommend something a little over $100 which also gives you an integrated camera and computer connectivity
EDIT: and look up some tardigrade videos on youtube, there's a lot of good tutorials on where to find them and the equipment they use