The amazing people at Wee Society have recently shared the most easy and inexpensive Halloween DIY costume ideas on their blog that you'll just love! All you need is some brown paper bags and few basic supplies that probably you already have.
You can download easy to follow how-to's PDFs for an owl, a fox, lion, and gorilla. The PDFs also include templates that come with instructions to trace and cut out pieces for the costume. Go here for the free downloads and complete tutorials.