Your first post in this thread.
Aside from learning about SVS, you also learn what is important in choosing a subwoofer. But, I can tell you right now that if you were serious about that $100 figure, you've got a long, hard search ahead of you.
First, get your basic system up and running. Then worry about a subwoofer. .In the meantime lurk here, read these forums, and learn about this hobby in the meantime. The
AV Research section of Audioholics has many, many articles that should be of great interest to anyone serious about learning about this hobby.
Seriously, I admire your wanting to learn and you seem like a nice kid but you've really got to do a little research on your own. None of us mind helping out when the going gets rough and answering a question or two, but you HAVE to do a little on your own.