Did you read
this topic and
this topic first? If not, read it and come back with some more specific questions.
I hate to burst your bubble, but it's going to cost more than $100 if you want to make a good looking costume that beats
the kind of costume that you can buy from Amazon. As an example, the first costume that I entered in a science fiction convention masquerade,
my Gamera costume, cost me at least $900 in materials and tooling. And a good-looking Predator costume contains a lot more armor than I ever had for my Gamera costume. So, if you're on a budget, you'll either have to make some sacrifices in quality, or you'll have to go without certain costume pieces.