My vet just gave me a HUGE money saving tip! I use Revolution on my dogs. At the vet, it's the same price if I'm paying for the dose for small dogs, or the dose for large dogs. So he had me buy the dose for large dogs, then just use a 1/4 ml of it. That way, I get 4 uses out of one tube!
I also use:
www.valleyvet.com &
www.revivalanimal.com