I bought some three drawer bins at CVS when they were on clearance... Drill holes in the bottom on the drawers and you've got yourself a triple level wet dry...
The easiest DIY overflow is simply a plastic juice jug hung on the side of a tank (with the handle) with a hole drilled in the bottom to allow it to drain (via pvc fitting/flexible hose) to the sump. Water goes into the juice jug via a couple of pieces of flexible tubing (via siphon).
What's even easier is a dump filter, which is basically a wet/dry in reverse. You put the rubbermaid (sump) above (on top of) the tank...pump water from the tank into the sump above it...and let the water dump back into the tank via holes in the bottom of the sump. I use them in many of my tanks. No need for an overflow or drilled tank. And you get nearly 100% of the capacity of your pumps because much less head is lost (than using a sump). I've seen nice looking ones built with plastic planters.
I ditched all of my commercial filters years ago!
Matt