The minimum bid starts at $0.001
Bid depends on ad format, TIER, ad spot and competition. The higher your bid, the more traffic you will receive.
You can find actual information while creating ad campaign:
We have 4 bidding options:
You'll get traffic at the lowest price, but you'll not cover all ad spots.
At this price you'll cover all ad spots. But in most cases you need to bid higher to win the auction.
As the name suggests, this is the optimal option for most advertisers.
Choose this option to be sure you will overbid all competitors.