The value of the minimum bid can vary daily, and is reflected by your targeting restrictions, and other Advertisers competing for that traffic.
There are 2 ways you can review your potential minimum bid.
1. When setting up your campaign and on review.
2. Using the Traffic Volumes Tool.
1. When setting up your campaign, under the Budget tab you can click on to see how your current bid stands in line with the average advertiser minimum bid. You can increase or decrease your bid to optimise your spend.
The Graph will show you your current bid in RED, the recommended bid in GREEN and the lowest bid for your traffic profile in ORANGE
2. Before you decided to spend time on creating a campaign you can estimate minimum bids required in line with the targeting you intend on setting by using the the Traffic Volumes Tool. This can be seen in the bid box in the image below.