Keeping things on the low end, since you specified $100 or less:
Maybe something like the
Kodak Playsport Zx3? About $90, it's an older gen, but can (ostensibly) record 1080p and has a user replaceable battery (a plus in my book). Also is supposed to have a fairly large image sensor for its class, which is generally important in regards to low light performance (don't know about actual performance, though).
It also uses SD cards, which has it's own pluses and minuses (one negative; I don't believe it comes with a card, and only has 128 MB internal memory. Not a big deal if you happen to have an SD card handy, annoying if not. Also, if you happen to go this route, don't use anything higher than a Class 4 card. Apparently the write speed difference can cause some problems, ending in corrupted video files.)
Minuses(IMO): saves the files in Quicktime format. Ehhh. Also, no macro mode, which may be important if you want to focus on costume details.
Some test footage:
Similarly, there's the
Kodak Playfull. Crazy cheap at around $60-70 (depending on the gen), it's supposed to do 1080p pretty well. No replaceable battery, but it does have a macro mode.
I might suggest the Flip, but looks like the parent company is pulling the plug on it.
Personally, I'd be inclined to save up and get a good point and shoot that also does video, but then I lika da pitchers.