This is a very broad question. First off what are your plans for the tank? Fish only,
FOWLR, or reef tank? Different equipment will be need depending on which way you want to go. For a fish only tank you could be looking around $500-600 with tank and stand. If you wanted to go with a reef tank, there is no limit to the amount you can spend on equipment. You can spend $3000 in lighting alone.
The best thing you can do is first decide what your ultimate goal is for the tank. Once you know that look around on this site and others to see what people are doing for there setups. In most cases you will need a tank, stand, heater, power heads, protein skimmer,
sump, return pump, overflow box, "unless tank is reef ready", sand "live of not",
live rock, and lights. Plus a lot of misc tubing and electrical connections. The big differences between the types of tanks are the amount of flow you have and the type of lights you have. Reef tanks will need more flow and higher output lights, where as a fish only tank will not little flow and less lighting.
You can get away with buying inexpensive things, or a lot of items off of ebay or craigslist, but just remember. In this hobby you get what you pay for. A $50 protein skimmer will not work as well as a $400 protein skimmer.
Hope this will get you started or at least give you an idea on where to start.
Brian