I have a 125 with a 30 gallon sump full of live rock (sump). I need a small skimmer to fit in the tank. Don't see much on Craigslist. Could use a small quiet one.
I would recomment a marine pure bio block in the sump instead of all that live rock (maybe sell it to offset the cost) and when you do water changes stir up (after turning off the return) the sump and changing that water. The rock down there will just trap detritus and potentially lead to issues down the road.