There is no way you could really know how much money would be made through Google and Yahoo! ads. There are too many variables.

Take Google for example, which would be Google Adsense.

First of all, they do not really tell you the percentage of money they are going to pay you. They just pay you part of what they get from the advertiser. So there is no way to know exactly what percentage you get from the advertiser. People assume it is 50%, but that is not the case.

Second - it depends on the market/niche that your site is on. For example, Weight Loss would be much more lucrative than Cat Toys. Advertisers in the Weight Loss Market pay much more than Advertisers in the Cat Toys Market.

Your conversion rate (the rate at which people click on your ads) will depend on many things as well. Ad placement, ad color and layout and much more. On average, you could earn a 1-3% conversion rate.

So if you get 1000 visitors per day, then you could get as much as 30 clicks per day. Sometimes your conversion rate might be even higher (it all depends on the topic and all that other stuff), so maybe you could have a 10% conversion rate (very high way above average), and that would get you 100 clicks per day. The amount of clicks you can get is easier to estimate.

The problem is that you could never know how much you will get paid. You can use Googles keyword tool in order to estimate, but even then - its hard to tell how much you would get paid.

Most of the time it is anywhere from $0.03 per click to $0.50 per click - and sometimes (once again depending on the topic), you could get as much as a couple of dollars per click. Back to the averages, if you have 1000 visitors, and you get $0.10 per click, then you would make around $5 per day.

If you want to make money from a website, this is the worst way (easiest, but not the most lucrative). Go directly to the advertisers, and you will make more than double for your traffic.

ADDITIONAL DETAILS: * It would be the right thing to start with Google Adsense or a similar program when just starting out. Except, your question was about how much you could make - so, although you could make a lot with Google adsense (with tons of traffic), you would make much more with private advertising.
References :

Some AdSense publishers will tell you that they make far more than $10,000 a month and they would not be lying - however there are some really big AdSense hitters who make as much as $100,000 a month.

So how much money can the average AdSense publisher expect to make from this magic program from Google?

Well even if you are just starting out with trying to make some money from AdSense, there are a few key things that could influence how much you actually end up making.

For instance if you are in a niche that does not have a great following, ie is pretty dull and uninteresting, not only will you not get the traffic volumes you need to make decent money, but Google probably won’t have enough advertisers (or even any advertisers) who are willing to pay for ads for AdSense to be served up on your website.

Then on the other hand you may be in a wildly popular niche where the amount of AdSense publishers is not a factor. ie there will be many ads available to be served up on your site, but believe it or not getting enough traffic will be your problem.

How can this be when I’m in a popular niche you may ask?

Well this is because the very nature of your niche’s popularity will make it difficult for your site to be ranked highly in the SERPS (Search Engine Results Pages) which in all likelihood will result in your site being consigned to the bowels of the Google results pages.

Hope this helps you!
References :
http://www.DuplicateMySuccessSystem.net