Sponsored search ads at yahoo was fixed before to .10c today they changed it by value and quality of keywords. In other words its like an Auction

Something in their words:

Starting today, minimum bids for some Sponsored Search keywords will no longer be fixed at $.10. Throughout the next week, you may start noticing new minimum bids on some of your keywords. Your new minimum bids can be lower or higher than $.10. Content Match minimum bids currently will remain at $.10. We’ll notify you in the account interface when the status of any of your keywords is affected.