Step 3: Material Acquisition: Buying Recycled Stuff.
Finally, dumpsters are far from the only place to find things. This project requires some things that you will never find in dumpsters -- like working light bulbs. For this, look to places which explicitly work in recycling. In my community, Habitat for Humanity ReStore is a fantastic resource. They had the paint I wanted, the halogen light bulbs I needed, and even a light fixture that worked to hold my lightbulbs, all for profoundly reduced prices. You can find the HDPE you need in the form of cutting boards at thrift stores. And you can also ask friends and family if they have extras. Chances are, they do or they know someone who does.
Another great spot are hazardous waste recycling facilities. Mine has a "materials exchange" where you can get paint and glue for free.