Can a non-professional drill holes in a granite countertop?
I am a granite top fabricator, and every time I drill a hole in granite or marble, it always scares me. I think, "what if I crack this top by making the slightest error; I better pay attention and take my time!" Because the slightest error can break your stone top; even with experience it is nerve racking.

First you need a hole saw guide. Cut a guide hole with your hole saw out of a scrap piece of ceramic tile or a thin 1/8" to 1/4" piece of wood and clamp it or have someone hold that with two hands firmly. With this guide, start your hole dry until you cut down about 1/16" to 1/8 into the stone. Then, remove guide and now you have your starting guide to finish your cut. Cut slow and have some one with a water bottle applying water at all times. Though, put a sponge on both sides of the bit so you don't make a mess. If you already cut out your plywood, be careful when you get to the end of drilling your hole because you can easily plunge your drill through the hole, slamming the drill onto the counter and breaking your top. Remove your guide bit on the hole saw and pre-cut your plywood with a wood hole saw with guide bit.

Not to many people are successful their first time without a pro by their side so good luck! Or you can keep calling granite guys for a better price.