After much searching, I finally found Mexican River Rocks in my city (Indianapolis) - we're going to use the 2" diameter rocks for a 40 square foot bed. The rocks come in 75lb bags - Can anyone give me an idea of the number of bags we'd need for a layer approximately two rocks deep?

Not only are these rocks expensive, but they are on the other side of town - I don't want to have to make repeated trips, but I also don't want to plunk down too much money for rocks I don't need! Any advice is much appreciated.

Cheryl in Indy