This works great on fleas short term and cost effective

Natural Flea Control: Oil of lavender is said to be effective and safe as a way to get rid of fleas and keep them away for the short term. Using a dog brush as the guide, cut a piece of fabric (like an old towel, cotton material or even several layers of old panty hose) larger than the "head" of the brush. Dab on several drops of oil of lavender and then scrunch the fabric together to spread the oil around on the cloth. Put this over the brush head and press into the bristles. Brush over your dog’s coat, rinsing the brush in clear water if necessary. This is a nice way to "freshen" the coat and help de-flea at the same time.