On a 75 I would defiantly run a sump. On a tank that size even fish I only it is still going to cost a bit unfortunately! It is always best to get quality equipment from the start, saves you later down the road when you need to replace everything. Is it you first saltwater? Put an ro-di system on top of your list, good quality protein skimmer (rated for twice your total water volume) 2-3 powerheads and all the bits you need for a sump - that's were I would start...