J.C.
My son has always been pretty opinionated about what he wants to be. But I have found really great cheap costumes at GoodWill. This year we got a tigger costume for $5 in perfect shape.
The costume rack right now has lots of options. When my son was that old I dressed him as a pumpkin with orange sweats, orange sweatshirt and a green jack-o-lantern face. He was very cute and warm, and could run around in it. He wore it regularly until the elastic on the pants stretched out too much and he outgrew the sweatshirt.