LF - Skimmer good to 400 gallons

[FishyFishy!]

I'm looking for something that is in sump. Space isn't a huge issue, I have about 20"X20" of space for it (footprint). Something good to run 400 gallons of total water volume would be nice, but not 100% nessessary. It will be a heavily stocked tank eventually.

Display is a 160 Gallon 7.5 foot tank. The filtration sumps total about 110 gallons, 20 gallon frag tank, water change/live rock tank about another 50 Gallons, and then a 30 gallon cheato fuge are all on the same system. So realistically something rated for between 300-400 gallons would work.

Just looking to try to save a buck by buying used, because that means I can put more money into other things in the build. I may just cave in and get the big CSC skimmer or the RLSS r10-i new. Whats a few bucks anyways these days!