From Anime News Network:
"Cyber-Stein" an extremely rare and powerful Yu-Gi-Oh! card is currently on auction at eBay with the current high-bid at $25,300 at 39 hours remaining in the auction. Currently there are only two English Cyber-Stein cards in existence, both of which were given away at last weekend's GenCon SoCal (one to the Shonen Jump Yu-Gi-Oh! tournament winner, and the other to a raffle winner). While there are no plans to mass-produce the Cyber-Stein card for sale, future copies will be given away at similar convention, with the next ones being given out in February at the Shonen Jump Yu-Gi-Oh! TCG Championship in Las Vegas.
The Japanese version of Cyber-Stein occasionally shows up on eBay and is auctioned off for less than $50. The English card however is legal in North American Yu-Gi-Oh! tournaments.
Cyber-Stein is a monster, DARK/Machine/2/700/500, and its effect reads: "Pay 5000 Life Points. Special Summon 1 Fusion Monster from your Fusion Deck to the field in Attack Position." Now, there's only one Fusion monster worth paying 5000 Life Points to get on the field -- the Blue-Eyes Ultimate Dragon, with an ATK of 4500 points (which hasn't yet been released in the US, although there have been rumors). I use it in my GameBoy Advance deck, and it's a very powerful card, but also very risky -- you either get your BEUD out and trounce your opponent with it in a couple of turns, or else your opponent manages to destroy it or send it back to your Fusion deck (with Man-Eater Bug, Penguin Soldier, Raigeki, Mirror Force, or any number of other cards), and then you're pretty much toast -- you're down to 3000 LP or less, and you've lost your big monster. Either way, the game is generally over pretty quick after you play it.
I don't really like playing it -- I think One Turn Kills are kind of boring, and rely more on the luck of drawing the right combo of cards in your hand than skill -- but I'm at a point in my GBA game that my opponents all have way better cards than I do, and the Cyber-Stein/BEUD combo is one of the few advantages I have. I'd really rather have a couple of Gemini Elves or Goblin Attack Forces. (Yes, I could use the password to enter these cards into my GBA deck, but I prefer to play using only the cards I get in the game. It's more of a challenge.)
Anyway, I thought the Card of Sanctity (a spell card that allows both players to draw until they have six cards in their hands) that sold for over $5000 on eBay a few weeks ago was outrageous! I can't imagine paying over $25k for a card.
(PS - checking the auction listing further, I've just noticed that the listing says that bids from people with feedback ratings of 10 or less will automatically be cancelled, and the current high bidder has a feedback rating of 8. So the current bid may not stand -- we'll see! As of now, there's still a day and a half left in the auction.)