CTR and click cost

How long does it take to get click cost down?

[vphoner]

I am relatively new to MSN advertising. I would like to know how long CTR takes to get your click costs down to the lowest level.

For example, lets say I am bidding .50 per click to get to the #2 spot in the blue. And lets say within a day or two, my CTR is 20% and continues at that level for the next couple of days. How long will it take for my price to drop to the absolute lowest level (all else being equal). Will it take a day or two, a week, longer?

Is the formula for CTR based on quantity of clicks by the other bidders, or weighted toward past and current clicks?

The reason I would like to know, is because if you reach your lowest price in a day or two, then you could determine if it will be too expensive. But if it takes longer, than someone could be more patient and wait till the price per click drops more.

Thanks...