No offense, but in this case Dilbert is just being a jerk.
Most PHB would not even ask for your input on the budget. Leading for under-budget projects. In the unlikely event that Dilbert project really needed 1 billion dollars, showing why would have being a lot more productive than acting like a childish jerk.
In my experience, you are normally told what budget (and headcount) you are getting and then need to provide extraordinary justifications if you want it increased. It may work differently at levels above mine.