You don't say where you saw this price, but if you check out the GS website here
you'll find out the cost including shipping.
I seem to remember that (1) GS members receive a mail invitation before the end of each year to buy the new edition, and (2) I think you can pick up a copy from Camping World and avoid paying almost $10 in shipping costs.
The directory is a "must have" IMHO.
Edit: Just opened my mail and found the invitation to order the 2008 directory. For GS members, $12.45 + $4.95 shpg + $0.90 CA sales tax = $18.30 or order 2 for a total $31.66.