For this Cat in the Hat homemade costume I used thin foam off a roll, the sort you can use for packing (donated) to make the hat. I drew out the stripes then used acrylic paint, and used white glue (I needed some staples to secure it as it takes days for the glue to dry).
The rim was a circle I drew and cut out the middle into triangles leaving them to glue inside the main part of the hat. I then attached a shoe lace using electrical tape to secure it. I made the bow by printing off a template and gluing it to some more foam and attaching a shoe lace with electrical tape.
The headband and paws were loaned from a friend, but I am sure they can be purchased from a store. My daughter wore her own black leggings, white top and black cardigan. I tied her hair into a bun and then painted her face.
This outfit won for her class Y6 in the book week 2010.
Cost: Nothing, all donated.