Agile Budgeting and Contracting

How do agile projects accurately forecast their budget when they are typically just a bunch of hippies coding without requirements or documentation? Waterfall projects are obviously much better at budgeting with all of the traditional up front design and planning, right? Anyone who has been on a waterfall project can see that this is a complete fallacy. Good agile projects are typically very accurate with regards to budgeting.

Video Producer: Pillar Technology