My highest was around $5.50. It must have been a fluke because my average clicks are about 50 cents each. Probably some newbie trying out Adwords.
I have seen this same question many times here on DP. Why do you not use the search box? I bet you will find it very helpful.
I got one for $5.21 today and they usually only average about $0.30 for my niche. So it was probably just a noob to adwords.
2.15$ so far, but I usually don't pay attention. I mostly just watch the count for the day since you have to do some subtracting to figure out how much the last click was...
It was actually about 2.57 and I guess you wanted to know what it was ... Im almost sure credit cards carry the highest click value