internal filters

Hi guys, I recently got a 2nd hand AquaMedic Percula 120 for free from a local guy who was downsizing. The problem is that it has a sump built into the back of it that takes up a good 48" x 6" x 24", so i plan on just using canister filters so my fish can utilise the extra swimming space...

Just checked the price of EHEIM Classic External Canister Filter with Media. Its is around $ 87.57 in Amazon! Is it worth buying? The cheap internal filters serve the same purpose, so is it worth spending that much money on eheim filters?