Here's a week on my best Adsense site which is in the payday loan niche:

Page impressions: 5,567
Clicks: 381
Page CTR: 6.46%
Page eCPM: $139.59
Earnings: $810.74

Over the coarse of a week it works out to over $2 per click, so that should give you an idea of what is possible. The key to make that kind of return is having highly targeted/ high quality (from search engines) traffic.

To sum up earning with adsense, you either need massive traffic for a more general topic, or quality traffic in a profitable niche.

If you are going after high value traffic - you'd better know your SEO.