digital microscopes are a lot of fun, and also very convenient considering you can record what you see on the computer, and post it here for help. It's very difficult to record down through the eyepiece, so it definitely helps. It also means you don't need to use the eye pieces either.
You will want a compound microscope (monocular or binocular- your preference) that magnifies 40-400x magnification to see all you really need to see, however a lot magnify 1000x and over which is great if you ever want to start doing things such as bacterial stains in future.
Microscopes with built-in digital components are more expensive, however you can buy a microscope that comes with a viewing camera which attaches through the eye piece. Just as functional, but from seeing Helen's videos (we have the same microscopes but helens has a built-in camera) the ones with the built-in digital components are better quality. They are both good quality cameras, though.
All of these binocular microscopes have suitable magnification so you can have a look through them. 1.3MP is the camera component mine came with which produces a good quality image, however you can get higher MP ones.
If you're looking for $100 and under, ones like these are suitable and have good magnification but are not digital. With that being said, you can buy digital components for them.
And here are digital components that will fit these microscopes. I personally wouldn't get less than 1.3mp because it gets a lot harder to see moving microorganisms and identify them on video. I upgraded from a 1.3mp to a 3.2mp which is fantastic quality.
This is just one website out of many you can look at, including amazon, however I hope it gives you some options and helps narrow down your search for one. If anything, take your time and even youtube the microscopes with digital components so you can get an idea of the video quality.