I speak for everyone when I say this: If you want people to take your question seriously, you should probably put some more meat on the bone.
Well it depends upon the number of clicks you get from your google ads.and also on the keyword which you are targeting.
You want us to set a limit? Who really cares, go much as much as possible. The limit is 100000000000000000000000000000000. That's how much you can make, now go do it.
depends upon niche and also on the country region in which you are.you will get more money for the same number of clicks in U.S.A an Ausralia than in asia.