Budgeting a project can be a bit of a you-go-first, no, you-go-first dance. The client wants you to tell them what the project is going to cost and you want to know how much they have to spend. One way to handle this is to explain that any project, from a simple letterhead to a corporate brochure, can cost as much or as little as can be imagined, and what you want to do is design the best and most creative piece possible, within the natural constraints of their budget.
Tell your client you understand that a start-up or non-profit is going to have a different budget from a multinational corporation and you will do your best work if you have some idea of the parameters up front. Even a range or a not-to-exceed amount is helpful. Explain that you can use these guidelines to schedule time appropriately, to think of effects that are manageable, and to allocate resources between creative, production, and printing so everyone gets their fair piece of the pie and, most important, the client gets the biggest bang for his or her buck.