umm I think the main important thing would be having a realistic looking tail. I'd say find a stuffed like this one.
http://www.city.ames.ia.us/shelterwe...th%20leash.jpg
cut it open and take all the stuffing out of it and put grease all over it (or anything that's black and dirty looking). You could spend like 60-70$ on a totally realistic looking cat but I think you can really do a good job with the not so realistic looking one. Hope that helps ya :)