There are some kits out there that sell something like a berkey filter, 2 - 5 gallon buckets and spigot.
What would happen if you took 2 - 5 gallon buckets, put a single black berkey filter in the top bucket, then filled the top bucket with sand?
Drilled a hole in the lid of the bottom bucket...
My wife found this on another site. Take a look.......... I think it could be done a little cheaper with some ingenuity.
http://www.alpharubicon.com/kids/homemadeberkeydaire.htm