Eh, trial and error might be the only way to determine for sure...
I have sites that get 2,000 a day but make relative pennies, and sites that get 10's of visitors a day and do considerably better.
Depends on the topic, the nature of the site, like you said.
My best bet would be 500 a day for a topic with "high priced" clicks, 2,000 - 4,000 a day for a topic that doesn't command high enough premiums.
-Allan
