You will find that the cost of an in-ground fiberglass swimming pool varies by location, shape, size, and decorative quality of the finish and surroundings. The typical 12' x 24' rectangular (288 sq.ft. of water surface area) fiberglass pool will cost around $78 per square foot. Typical extras raise that cost to about $109 per square foot. The Total Cost shown above includes the five-man crew that will be on the job a total of 160 man-hours, or four days.