there are better ones to buy than an eheim that you can change around at a later date !
but also you can make one for less than $50 it really easy ! i made one for my puffer tank using a tall kitchen garbage can cut holes in the bottom placed it in a rubbermade tub ! fill with bio balls ! i made a drip plate using a old tupperware dish and heated up a file and poked a chit load of holes in it !! has kept them alive for a few years now !