Amazon will increase your bids in real-time for clicks that may be more likely to convert to a sale, and reduce them for clicks that are less likely to convert to a sale.
So how much could you end up spending? For example, if you have a bid of $1.00. For top of search, this bid can be increased by up to 100% so that would be a maximum of $2.00. For all other placements, the maximum is 50%, so that would be up to $1.50.