Sky's the limit in this hobby ... but don't let it discourage you. I've seen some beautiful reef tanks that have been put together on a budget.
Lighting and Live Sand (LS) and Live Rock (LR) will cost you some buck$.
Sump / Pumps / Skimmer / if desired also add$ up.
Corals aren't cheap - but you can start off slow and add as you gain experience and can afford more.
Accessories add up as well - test kits, salt mix, RO or RO/DI water treatment ( or buy water ), supplements/buffers/calcium etc ...
The tank, stand and heater are actually not the most expensive items.
You could get a moderate start on a reef tank for about $500.00 bucks
But once you've been bitten .... it's all over <img src="graemlins//urrr.gif" border="0" alt="[urrr]" />