I purchased and started building with a 4' x 8' x 1/8" 3-ply piece of plywood normally used for floor underlayment. At ~$11 it was affordable, but I have gotten several small splinters in my fingers while working with it. I am cutting it with a hand saw, then sanding it with a belt sander. So far I have cut and glued together 14 pieces for the two supports that will be above the circular joints. I will be cutting at least seven more pieces for the support below the joints.
I have cut 14 acrylic circles: qty= 8 at 7.5", 4 at 8" and 2 at 8.5". These will hide the PEX joints and diffuse light from the WS2811 6-LED modules. I shopped on eBay and purchased qty=15 200mm pieces of 6mm brass tubing for cutting standoffs at different lengths. I plan on putting long wood screws through these to provide support for the acrylic discs.