if your looking for a good bass under 100, dont even bother. there arent any. but for metal and punk, id go with a fender precision, plays great, cant go wrong with it. hefty price, but you can do so much with it, jazz, rock, funk, metal, anything

I just bought a Squier Jaguar bass last week, and that's pretty good

I like playing Fenders. Maybe get a Squier Precision Bass. They're pretty cheap and easy to start on. My suggestion would be to just go to a music store and play a bunch

u should spend a little more on your instrument and get a used one. that way u can get a decent quality bass for cheap. but yeah, no amp = not worth it. and u will have to buy a case to take it with u, strings every now n then, polish...
if u r not ready to spend money on it then don't do it.

i would recommend getting a cheap japanese model of a famous brand. that way u know that at least some quality control was undertaken. later on u can replace the pickups if u r not happy with the sound.
some random cheap brand is pretty much out of the question. i would only recommend that if u were an experienced player as u will have to adjust things u r not familiar with yet.
I usually buy cheap guitars just to customize them myself.

Well at first you wont be able to play most punk and heavy metal. And you also need an Amp. So 100 bucks wont be enough. Cheapest guitar brand is Jack and Danny.