Well, I take it that you mean you need to buy the tank and all, without a previous saltwater set-up to get media and life from.
You'll have to buy the tank. (not sure how much 75g runs for).
Lighting (depending on what you put in the tank, IE corals).
Live rock (generally runs for about $8 U.S. so, youre talking about $600 just in live rock).
Corals. They run in all different prices. I've seen as low as $20 and up to $300.
Livestock. Again, large range if prices.
Equipment. Powerheads, protein skimmer, lighting. Depending on the quality, you'll pay a range of prices.
As you'll see in one of the pinned topics in the Marine section, this whole thing could run you about $1,000 to $3,000 as a beginer. I started with a Nano reef and its a handful and a pain sometimes. So if thats how you want to start, it will certainly be cheaper, but more work. Mine has cost me about $300 so far. I'm not finish though, so even more money is envolved. Keep up the research and good luck.