How to kill fleas,on animals,cheap?must be a method to make cheap,that works and is safe on animals.
In a pinch, Dawn dish liquid will work. Much better to purchase a proper shampoo. Completely ineffective unless you treat your home and yard.
first get a flea comb, second, get flea powder. Follow the directions on the bottle. there are flea shampoos available. you will need to do a second treatment as the flea eggs hatch.
You may need to treat your yard as well. Here are some tips: https://www.craftylittlegnome.com/kill-fleas-in-the-yard/
We used to sprinkle brewer's yeast (ground-up tablets) on our dog's food. He never had a problem with fleas. You may have to stir it into his food if he is a persnickety type.