First, you need to buy the sink.
Is this a kitchen?
I recenlty installed an undermount Kohler Cast Iron Sink and granite countertop. (A few months ago.) You buy the sink, and you need a mounting kit. Basically, the mounting kit is 2 steel bars with a series of slots in them. The bars mount to the cabinetry, or you build a frame and mount the bars to the frame (which is what I did.)
There are a series of set screws that adjust the elevation of the sink up or down as required to bring the top side of the sink flush with the underside of the granite.
The cost of the granite depends on the slab you want (pattern, colour, texture (they have textured granite now). Costs can vary significantly.
I highly recommend Custom Granite in Stoney Creek. They did my granite and it looks fucking amazing.
http://www.customgraniteandmarble.ca/
2 different people recommended this place to me. I live in Toronto and didn't feel it was worth the drive to Stoney Creek, but when 2 different people told me to go there, I figured I'd check it out.
They have an amazing show room. You go with your measurements, they will take your measurements and give you a price list by group. Group 1 through 8 and there is a price for each group (supplied and installed). Then you go pick which slab you want.
Then, they come to your house and make an electronic template (a mini total station). You need to have your sink in place at this point in time. The guy will shoot your layout to the mm, draw it in autoCAD, then email it right to the factory. 5 days later, they are there installing the slab.
My fit and finish is perfect. I wouldn't have believed it.
What I liked about these guys was that they have thousands of slabs on site, they measure, they fabricate, they install. So many other granite places don't do everything. They will do whatever edge pattern you want, and all their slabs are 1.25" thick as opposed to 3/4" with a built up edge (superior). They also did my L shaped granite in one piece - no seam in the corner which is again superior.
The price was better than anywhere I was quoted in the GTA (went to 2 places).