Maybe you could go as a cat-wear all black and paint your face with one of those face painting kits. You could stuff a black nylon stocking for a tail?? Make some black ears out of felt and glue on a head band if you can't find one already done. Paint a cat face with white and black paint. Wear black gloves.
I don't get into Halloween too much and I can't see buying/renting a costume for a lot $$$. I am sure there are alot of creative Low carbers out there that will probably have better ideas, but maybe this will get you started?? Have fun!!
MKay