What type or filtration would be best for a 30-40 gal brakish tank!?

im going"shopping" on the 30th and i need to know the type of filtration nd air flow that would be neccarsary for 40-30 gal brackish? basically what would be every thing i need for a brackish tank besides the tank-fish-live sand-heater and what not, like i want to know from people with expierence with a similar sized tank on everytihing the it would need to be "brackish", i want to know what i need to check the ph and and know the salinity, i need to know the type of power head ands different canister filters i need to get to make this the tank iv been wanting. also i was wondering from poeple who have gone through with all of this if thi is going to be under 200? since i have what i think most of what the tank needs, or is this going to cost me an unexpecting fortune...which i have already spent.

i already have 2 GPS's but im soon going to be upgraidn tothe tank and not for a couple of onths is when it has to be fully brackish.

for a 30 gal how much would that cost? and what im wondering if theere is a special one i need for brackish?

and yes i know im planny on getting at least a 50 i dont think i could go to 60 right now...