The monitor I used inside BMO was $5 at a yard sale. I needed a 4:3 monitor to keep the correct aspect and went to a few yard sales looking them.
For the legs I used PVC pipes. Then I laser cut wooden circles and used Gorilla Glue to hold the thread rods that attach the feet to his body. I drilled a small hole on the wooden circles to run the power into BMO and not have an ugly cord hanging out. I foam filled the PVC tubes to add structure and support to the rods and pipes. I 3D printed BMO shoes and hands. For the arms, I just bought a clear hose that had the scale of the BMO arms at the local hardware store. Then I Plasti-Dipped them and painted them blue. The shoes allowed about 3 inches of the PVC to extend into the box allowing me to use hose clamps to attach BMO to the CNC base with the Adventure Time logo.
The picture of the inside shows you how I attached the speakers using hot glue and supporting it with a 2x2. The Raspberry Pi case is attached to a 2x4 by 3m double stick tape.
Finally, as seen below, BMO was a total hit at the Miami Maker Faire. The kids immediately recognized BMO and came to play video games while the adults came to reminisce and play their retro favorites!