The best advice I can give is get a minimum of three prices and check references! A simple search on google can get you started...See reference below.
Depending upon the topography of the land the cost can really vary. In MA you need approx. 6 feet from the bottom of your leach field to your ground water so that has a tremendous impact on the cost of the system. I recommend having the land perked and then go from there. All the best.