Infant car seats are the norm for brand new babies. They offer the convenience of easily moving from car to house without disturbing a sleeping baby.
If you are looking to cut costs consider buying a convertible car seat and use it from birth. Many, such as the Britax Diplomat or Boulevard, already come with infant padding allowing it to support a 5 lb. baby. These car seats have a weight limit of 40 and 65 lbs. It may be the first and last car seat you buy.
The Diplomat retails for $250 and the Boulevard retails for $300. Sprout in Brattleboro, VT is a Britax retailer as is Kiddo in Hanover, NH.