To answer your question directly, You'd need a lot of clear epoxy suitable for a 3/8" pour depth. This would be your main cost.

Then, you'd be best-off picking up either hexagonal washers or low-profile hex nuts. You'll run about $3.19 for 100 of them from McMaster-Carr (Product 91078A205 )

Technically speaking, they're cheaper than pennies. About 3 times cheaper. The nuts will be only about 0.45" across, though.