Quiet Wave-Creating Machinery

I'm seeking a specialized piece of machinery to create waves in a waterbed mattress. The mechanism should ideally be a crank and slider, converting circular motion to an up-and-down motion, repeatedly pushing down on the mattress... (Budget: $250 - $750 USD, Jobs: CAD / SolidWorks, Engineering Drawing, Manufacturing Design, Manufacturing Engineering, Materials Engineering, Mechanical Engineering, Product Design, Product Development, Prototyping, Solidworks)