here's a link to mops for salt. Not sure if it's a good price or not as I am a FW person, just figured I'd share....
http://www.aquariumsupplies.ca/specials.php
It's a good price but I think with shipping it comes to pretty much the same if not more expensive then if you were to get it on-sale locally from one of the sponsors but I may be wrong I am pretty new to salt
Make sure there's free shipping on that 50lb bucket of salt :P
The shipping makes it more expensive than the regular local price.
Like I said, I'm a FW person. You would have to contact them about the free shipping. Not sure if it is on salt as I have never ordered it before.