The fiberglass/resin part won't cost you $100, but all the other stuff you can add to the suit piles up fast (LEDs, helmet liner, fans, visors, etc.).
Yer, read the stickies in the Pepakura forum, everything you need to get started is in there. Make sure you've read through them and utilized the handy search button before posting new topics on questions that have readily-available answers. Pay attention to the construction threads from folks who are actually in the process of building armor - you'll pick up a lot of tips and tricks, not to mention the fact that you'll get an inkling of the true cost of pep armor in terms of supplies and time.