So take some basic measurements and go price some granite. You will notice a wide swing the the price per square foot. This is not based on quality, but rather on the rarity of the granite chosen. Choose what you like, even if it is the less expensive slab.
At most places granite starts at $50.00 per square foot. Home Depot often has sales where it starts at $39 per square foot. These prices include installation. But don't fooled into thinking that is the final price of your granite. That price covers only the granite, measuring the template, cutting your granite and installing it. What is not covered is what you need to know about.
Before they will measure for the template your current countertops need to be removed and you base cabinets need to be leveled to within 1/16". This means that your sink needs to be unplumbed, countertops removed and leveled. This is not covered in the installation price. Also, you will need to have purchased you under mount sink. They will need the model number when they measure for the template. You should also not that there is approximate cost of $250 to attach the sink to the granite when they install the granite. Attaching the sink does not mean that they plumb it. So, after they measure for the template, if you want to use your kitchen over the next couple of weeks you will have to re-install the sink, plumb it, and re-install portions of your countertop. These items are not included in the price of your granite per square foot install.
The day before your granite arrives you will need to once again remove the countertops and sink. They will then install your granite and attache your sink. Now you must have your new sink plumbed which means you need to install the faucet, new strainer sets, new garbage disposer, new trap set, new water supply hoses, new soap dispenser, attach the dishwasher, the ice maker, and sometimes install new water supply faucets. These are all added expense.
Is it all worth it? In our case, yes, it was. We love the look, the durability, and the overall value it adds to our home. The important thing is that you go into this with your eyes open and don't get caught off guard by the extra expense.
Feel free to ask questions about home repairs and remodel. I'll do my best to answer them here.