Regardless of whether you are relying on an installer or are planning to do it yourself, before ordering counter top material, you should consult an expert, like one of the many here at green by design. There are a few questions to think about along the way:
Is my sink a drop in or an under mount? Does your sink have a "lip" edging out over your counter, or does it just install under the counter top and fit perfectly? If it is the latter, the estimate for installation will be higher because the sides of the surfaces running alongside the sink will need extra finish and polishing.
Edge Detail? Do you want a fancier edge do you want to keep it simple and polished? A more detailed edge will also amp up the cost of installation, so it is important to factor this in when selecting surface material.