Help with Salt Water fish tanks?

I'm about to start up a salt water fish tank. I have all the filters and heater and whatnot to use already. It's a 40 gallon octagon tank. I guess my question is what's the best way to get all the supplies such as salt, sand, testers, ect.. I don't want to spend a lot of money on this, just a live rock with a few fish for now. Is there a place online where I can buy everything in one kit?? That would probably help the most instead of getting ripped off by a pet shop. I have helped my brother set up his salt water tank but he bought all of the items individually.