Here is some ideas:
http://www.ozreef.org/diy/index.html#SUMP
The only thing I can suggest to you is that you need to get an overflow box before you consider a sump. I have been trying to build my own overflow boxes but it looks ugly and there is always a chance that it might not work and can cause a flood. Buy an overflow box on ebay for ~40$ and get the biggest flow rate you can. Get for example a flow that has one inch diameter. Don't skimp on that because it's important.
O.K. you stated that you wanted under $70. Your overflow is already around $40-50. Your sump can be made for about 20-30$. Get the largest sump that you can fit under your tank. I got a 20 rubbermaid container for 7$ or get a used aquarium. There are fancy ways of putting plexiglass or acrylic baffles for filtration but that requires a little more work and a little more money. I put a 5 gallon bucket in the sump and drill holes on the side for water to enter the bottom. You can put media inside with eggcrating to separate if you wish. Add a submersible pump in the container and your set. It might look cheap but it works.
You should try to get an overflow rate that is much faster than your pump return rate because this way you don't pump water in the tank too fast. Even if you get an overflow box that is too fast, it will stop and break the siphon once you reach a certain level on the overflow box.
BTW, I just installed my first overflow and sump on my aquarium yesterday. Fun and it's cool because you can put everything in the sump: heater, Co2 reactor, filter media.
I think amiracle makes the cheapest overflow boxes and should be around $40-50.