One option for the amp platforms is to go to your local granite countertop company - the one that actually has the cutting and fabrication equipment - and ask them for the price of a couple pieces of 20" x 20" (or however big you want them) of countertop material with finished edges. They have scrap pieces laying around and hopefully they would charge a reasonable price for them.
You could then get cones for the bottom surface if you want (they are pretty cheap on Amazon) and you could epoxy them on. This would be a solid attractive solution.
You could then get cones for the bottom surface if you want (they are pretty cheap on Amazon) and you could epoxy them on. This would be a solid attractive solution.