Cost of 20' treated 10 or 12" piling?

we were going to do a small dock for a friend and were trying to figure out what pressure treated pilings cost - we could use about a 20' pile, either 10" or 12" in diameter - I think there are some lumber yards in the area that sell them but I was too late in calling, they're closed for day - does anyone have some experience in buying pilings & know approximately what they would cost each? Thanks.