Sand is usually sold by the ton, sometimes by cubic yard if they don't have a scale. The S&G (sand and gravel) pit you called probably doesn't have scale. However, a S&G pit shouldn't give you a "square yard" quote unless that can give you a depth the square yardage is based on. If they can't do that, buy from someone else.
Sand weighs from 2400 to 3100 pounds per loose cubic yard, dependent (for the most part) on moisture content. Because the sand will be compacted under the weight of the water in the pool, I would use a weight of 2970 pounds per cubic yard as a base, or 1.485 tons per cubic yard.
Be sure you get masonry sand as it has no gravel, which could create a hole in the pool liner.
There is a web site on pools with a sand volume chart you may be interested in here:
http://www.backyardcitypools.com/swimmi ... -Chart.htm