I'm on my fourth USB microscope, and while there are cheap ones around, you do get what you pay for. The cheaper ones are very hard to focus, claim higher magnifications than they really offer (by the convenient deception of talking about area magnification rather than linear (so when it says 100x it might only be 10x). You also need to pay attention to the stand, as if it is a bit wobbly, you'll be very frustrated.
The Dino-Lite range go from ~$150 to as much as you want to pay, but it's cheaper to buy one at the start than do what I did, buying successively more expensive but disappoint alternatives. I use it for other things as well as edges (and this is their cheapest):
Adjusting a cartridge
And checking if the stylus cleaner worked