I walked into TAP Plastics today. The sign on the door said:

"Scrap sale, 75% off"

I gained 15 pounds of HDPE, for $8. I think I’ll go back tomorrow for a load of acrylic.

[Update: another $20, another 38 pounds of plastic (~21 HDPE, ~17 cast acrylic); I may go back again if I can find someone working there who knows what some of the mystery plastics in the scrap bin are…]