Get bids from a minimum of three companies. This will help you compare the bids adequately. Note that contractors should bid only after visiting your home to check out the scope of the project in person.
Look at the price for the granite itself on each bid. Granite prices will go up as the slab gets thicker, so you need to keep the quality of granite in mind when comparing bids.
Check out the amount and cost of outsourcing for the job. A granite project can include outsourced work. For example, the granite needs to be fabricated. If a company has fabrication equipment in-house, they can offer a lower bid than a company that has to outsource fabriation. The quality of the end product will depend on the fabricator's ability to craft granite pieces.
Consider the labor cost. All bidding companies should include a cost of labor in their bids. Remember that installing granite is a tough project, so be wary of companies that have much lower bids for labor costs. Also, things like in-house fabrication will lower outsourcing costs but raise labor costs.
Read the bids carefully for added fees for the granite installation. For example, there might be a separate fee for installing a backsplash or for adding a higher-quality sealer.