The
SwiftTech MCP355 is a pc cooling pump that will do 20 ft. of head. Newegg.com has it for about $65.
Idk about using buckets, what if the flow rates are slightly different? could lead to an ugly overflow problem or one of the pumps sucking air..
Would it be possible to put multiple smaller pumps in series? maybe plumb them with the pumps at the bottom their own "U"?