I think a lot of people misunderstood you at first. This forum mainly focuses on movie-quality costumes for adults, and they are quite expensive. They are also way, waaay overkill for any kid.
Yes, we have to guys here on the forum who makes and sells kits for kids, but they are made using the same materials and quality of adult size costumes and cost almost as much. So unless you can get your parents to pay for you, you're going to have to stick to the cheaper options of cutting up foam pieces and glue them together to make a suit.