dont most pumps (i know mine does) sink and you put them in the pond itself, and decent pumps cost abit more than a fiver, you need one which runs the water through quickly to keep it clean, also, if you need 2 top up the water or anything, do it gradually as the chlorine in normal hose water can kill the fish, that chlorine goes away in a week so add abit of water each week if more water needs to be added.
could also buy a cheap water tester to test the water for shit and to make sure the water is neutral.