I found one! $79.99 digital, everything but the pump which I already have for when I do water changes. It has 2 floating sensors, one for the top off water tub and another for the aquarium.
You hang the one sensor where you want the water to stay in the fish tank, and the other you put near the bottom of the fill tub. As soon as water drops the digital thing turns on the pump, if the fill tank gets too low it won't come on at all, so the pump does not get damaged.
I just bought a skimmer. So I have to wait, so my mother won't go into shock for the top off thing. I already gave her a heads up that I need it.
She asked me when I can quit spending on the fish tank, when it will be all done...I just don't have the heart to tell her the truth....