Oh noez, I wouldn't buy hardware on ebay, at least not if it isn't completely new and sold by a trustworthy company. For 100$ you will hardly get a decent card I fear, the 7600GT is pretty nice and I personally wouldn't go any lower.
If it's your parents' money tell them 100$ isn't enough for what you are looking for, if they really want to help, they should get you a 7600GT.