Main use for a canister on a SW
tank is for flow, and carbon. You don't need filter media if you use live rock, which has quickly become the most common SW
setup. Its natural filtration, and provides the fish with a much more natural environment.
I'd spend that cash on a good skimmer. You can always use a cheap HOB
filter with a bag of carbon inside to get the benefits of carbon, and powerheads will give you all the current you need.