"West system" epoxy resin, used about 8.8 L, it comes in various sizes - the more you get the cheaper it is. For a 4.4L kit it cost $120 I then added a black pigment to darken the resin.
After about 3 coats on the front I sprinkled on 20 KGs of black silica sand ($54) and then ate the poly away with acetone, needed about 6 - 8 L (about $60 total)
and for a few reinforcing coats on the back I mixed in a filling powder ($10) to stop the mixture thinning out before it set.