Tap is a high-markup retailer.
Interstate Plastics near CalExpo/REI/Costco is good for acrylics. My skimmer used remnant acrylic pipe that was inexpensive. They also built my pentagon-shaped tank and only charged me an hourly rate, not a premium because it was a tank. They also have the corrugated plastic in black that is great for the sides, top, and back of the tank.