How to know how much CPC to pay?

Can anyone tell me how I could find out how much other advertisers are paying for for CPC at sites with adsense placement?
I want to start some adwords placement campaigns, but I dont know how much to pay per click. If I bid too low, my adds wont show, and if I bid too high, I will be paying more then I could otherwise get away with. If I could know how much other advertisers on paying for for placements on specific sites, I could just place a bid a little higher and have my ads show no problem.
But I dont even know if the ads shown on the sites are from direct placements, like what I wanna go for, or if their from the content network part of googles advertiseing.
So really all I want to know is how much I should pay for placements ads […]

Original post by WhiteAl