Make a bid under the current price

Hello

I would like to give the users of my website the possibility, to make bits under (or over) the current price. Not only that, they also should be able to make a bid, which is equal to the current price. We want to have it this way, because the people who created the auction should be able to see all offers and decide then, to whom they are selling their product (e.g.: the location impacts the decision).

Does anybody know, what I have to do, to make this possible ?

Best regards
Philipp