What I usually do is reverse the question. Since it's often times, very, very hard to ballpark things, I ask them what THEIR budget range is, and then let them

What I usually do is reverse the question. Since it's often times, very, very hard to ballpark things, I ask them what THEIR budget range is, and then let them know if what they're asking for falls inside of it. If it doesn't, I offer up ways to make the project fall inside of it, or what parts of the project are so risky that, while in theory they might fall within, they might also blow up the budget. Clients want ballparks because they need to know if pursuing a given project is worth their time. No one wants to spend hours putting together a project summary and working on detailed specs only to find is 2X or 3X more money than they have. And the same is true for the agency. Why am I going to waste productive hours spec'ing something there's no way I'm going to actually book as work?