This is a pretty old trick but I'll bring it up in case somebody here doesn't know it yet. Basically, you can add "+" at the end of any Bitly link to see the traffic it's been getting. For example, the other day I saw somebody renting their sig space for $50 a month. I checked bitly and one of their links had received less than 50 clicks in the last 30 days. So now I know the CPC and whether it's a good deal or not.