The higher you reach - the more you will grab!
There are too many factors to give anything that could be close to exact - but I'll try to offer a sense of how much
Almost any blog that gets a top ranking for a keyword that has reasonable volume should make at least a few dollars a day if you are showing visitors something that matches what they came for.
Every once in a while you should have a BIG HIT which may or may not last very long.
These sites can make pretty big money from 50 to 100 to 200 a day or even MUCH more in some cases.
The biggest of the BIG keywords can pay MUCH MUCH more than that but are also VERY hard to get to the front page. Theres no limit to how much those can make.
How much should your goal be?
It should be high enough to make it worthwhile for you to do what you do. Only you can decide that!