I would like to know where you have found a 5 gallon pail of Instant Ocean for $28 though. If the pricing is from a chain or on-line store, I'll switch for that price if shipping does not bring it to the $40 ish price I am now paying.
I think 80 pounds of live rock will overwhelm a 55 gallon tank. Since you want to leave some room for your octopus to come out and play, the 1 lb per gallon ratio works better.
I'd skip the TDS meter and the phosphate tests and the hydrometer and instead get a good quality refractometer. pH is usually measured more accurately through a meter, too. I'm assuming that you'll purchase RO/DI water to mix with the salt.
I assume you're not using a sump. How about using a canister filter and a good protein skimmer - I don't think you need the SOS skimmer as well.
Often people put a powerhead in an octopus tank.
I don't think this adds cost, just rearranges it a bit.
thank you all for the imput (: i switched the sos to a canister that only added about 40$ to the toatal and the extra live rock will probably go into a small tank shrip tank that my friends giving me -freebies are a wonderful thing-