do a lot of research on this. do you want a fish only tank or do you want to create a reef aquarium. the reef will cost you a lot more than the fish only. i started a 65g reef aquarium and i think i spent close to $2500 before i put anything in there. that being said you can start a tank for a lot cheaper. i went with higher end equipment and i also bought stuff that can be used in larger tanks if i plan on upgrading. here is a great place to start. good luck!
www.reefcentral.com