Define cheap? My overflow was bought used and ran about $100 new. A club member gave me a deal on it for 1/3rd of the cost. I've seen decent ones run around $50-$90 in LFSs. Look for ones that are a 2 part box...a section in the front that a U tube runs over the tank top and into the back section and a pipe that drains to your sump. You'll most likely need a gurglebuster on it and they can be DIY for a few dollars to $15 for a purchased one. Then you'll of course need a pump to return the water to the 5ank. The one I bought isn't cheap but I love it, I spent $120 on it (Eheim1260).