If your need a petsmart you can bring it a print out of what they charge on-line and the stores will match it. Also Fishtown sell Salt pretty cheap. Dr Forster & Smith was running a sale on I/O with cheap shipping, I'm not sure if they still are.
The problem with getting it on-line nowadays is the shipping is ver expensive, so your losting almost all of the savings over buying it in a LFS.
I got mine from Tony @ Reef Exotics (West Hempstead). If you can pick it up you can save the shipping. He has boxes of it and the prices are definately worth the trip.