You need a set of dice, a Players Handbook, a Dungeon Master's Guide, and a campaign settings.
Dice start at $3 for a cheap set. I'd go ahead and get a nicer set for $5 or $7. Or if you're deperate go online and use the online dice:
http://www.wizards.com/default.asp?x=dnd/dnd/20040517aThe books are $23.07 each at Amazon.com. You can however torrent them on PDF at Pirate Bay. I went ahead and purchased them though because I'm a nice guy.
Campaign settings vary widely depending upon how big they are. Heck, there are free one widely available just to get you started.
So you can get started for anywhere between free and $60.
Let us know how it works out.
--bog