How many 40 lb bags of topsoil are on a pallet?

Generally speaking, weight doesn't equate to volume. Off the top of my head, I would say it would take about 50 bags to equal 1 cubic yard. Also, to check this, a yard of soil weighs about 1 ton (2000 lbs).

So if you need 7 yards, I would have a local nursery, or supply house deliver the 7 yards of topsoil. In W. PA we pay about $22/yd delivered. Compare this to $2 - $3/bag: $750 - $1150 plus loading & unloading your truck (or car) and about 25 trips to the hardware (or wal-mart-boo).