Check out http://AquaHub.com. Good prices on their own and also Madison brand. If you are looking for a pre-built system, check out http://AutoTopOff.com for customized units. I used aquahub float switches for my topoff system, but if I didn't already have an Aquacontroller 3, I would probably have bought a topoff unit from AutoTopOff.com and customized it to my needs.
Mike
Mike