One further comment. A smaller diameter prop is much less critical than a larger one. I balance my props while I build and usually do a few extras, but 9, 10, 11, 12s it's not a big deal. My planes with 16 inch on up need balancing or they WILL affect the plane. As far as car tires... specious arguement. They have a huge diameter and weight and are not applicable to props. When I balance little props, I use superglue on the back side of the prop and hit it w/ fixer. a light sanding usally will make it perfect in less tham a minute total.
Mike