I think epoxy cure times can be affected by heat, but if you are at anywhere near room temp, it should be about what is advertised.
I've used the stuff you can find in the varnish area of hardware stores (sometimes you can find it in the sculpture/mold section of craft stores, but I think there prices were higher last I checked (but sometimes you can find decent x%off coupons in newspaper flyers)). Not sure off the top of my head, but I think something like ~$20 for about a liter/quart. It's usually advertised as being equivalent to 30-50 coats of varnish, and it's what they use to make those table/bars with stuff embedded in them.
I'm not sure how much you need, it's been a while since I've done this, so I can't even remember what amount worked for me. Adding the sand or whatever will increase the volume (obviously) but also make it harder to apply, and you'll probably end up using more. I haven't tried it myself, but I've heard people talk about using chinchilla dust. I think you can add concrete pigment to epoxy mixes, but again, not something I've done, and I'm not certain about it.