Get a metal rod or tube the size of the prop hole. It should fit snugly. Get two single edge razor blades. Stick the backs of the blades into a piece of balsa, parallel and about 2" apart. Level them by eyeball. Slide the tube or rod into the prop and set it across the blades. The prop will roll to the heavy blade. This is what we used to do before prop balancers.

Now, tell me why you're too cheap to buy a $3 teeter balancer.

Dr.1