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So if no one ever had a campaign for your keyword using the old AdWords, there's a good chance your minimum CPC will be $0.05.
But suppose someone had a campaign in the old AdWords for that keyword, paid for each impression $0.02, and got a click rate of 1 click for each 37 impressions. That means his average CPC was $.74 - so Google determined that the minimum CPC for that keyword in AdWords Select will be $.74.
Now suppose you decide not to use AdWords Select for that keyword but the old AdWords, and get a click every 20-25 impressions - that means you're paying a CPC of $.40-$.50, while in AdWords Select you would pay a CPC of $.75...