If it's less than an hour since you bid, you should have the option to withdraw the bid and replace it with the correct one. So I've heard - I don't do auctions either as a buyer or seller.
If not, you will have to hope the price doesn't go up too much - you would not necessarily have to pay $900, only enough to win the auction if the price doesn't go that high.
You could also contact the seller, explain the mistake and hope they will cancel your bid. But there are timeframes applying to that as well. I don't believe bids can be cancelled within 12 hours of an auction ending.
Failing that, you could refuse to pay if you win and suffer the consequences.
