$100 and good quality are mutually exclusive. If you're on a shoestring budget, there are a few options:
1) Do you have a smartphone? Most high-end and some midrange phones will take passable video. Not good, but passable. Tape it to a tripod and make sure you have lots of light. Believe it or not, I've filmed quite a bit this way. It's a pain in the ass but it does work well enough for showing off projects. I wouldn't want to shoot a movie with it, but you probably could if you were desperate enough. Depending on how good your phone is, this sits between 3 and 4 in quality.
2) Search the used market- Craigslist, eBay, et cetera. You do not want anything analog- even expensive cameras look like flax by today's standards. Similarly, any low-end to midrange miniDV camcorder is probably worthless- my ZR800 looks like complete garbage compared to my phone. If you can find a relatively new HDV camcorder, they'll give you pretty Dang good video. You'll have to deal with tapes, and good luck getting on for under $100, but it's worth a shot.
3) Get more money. For about $200, you can get something that will do a half-decent job. If I remember correctly, my friend's camera cost about that much and we shot several videos on it. They look pretty good.
4) Buy something cheap and deal with the low quality. There are ways to minimize the crappyness. First, use a stable platform. Cheap cameras have no shake reduction and they're generally light and hard to grip so they bounce all over. Tripod that flax. Second, use a ton of light. You don't want so much that all you get is glare, but more light reduces noise. I generally use a pair of 300W halogens in a worklight for this. Third, you may need to dub the audio over after or record it separately, since again cheap cameras generally have flaxty audio. Or, if you're feeling adventurous, mod a mic jack in.