If you want to save the most money, you can use 2 AC 110's on your 75g tank. People usually sell them on MFK for about $30-$40 each. You can make your own wet/dry too using a plastic tub and pump, but I think they're noisier than AC 110s. And I always worry about the sump overflowing during a power outage. If it was my tank, I'd just buy an FX5 and be done with it. No need to worry about buying a pump and setting up the overflow or anything. It's less bio than a typical wet/dry filter, but for a 75g it's more than enough and makes things easier IMO. Plus, FX5's are always in demand. They have a really high resale value. I bought mine for $230 and used ones on MFK go for about $170-$200.