NSA's budget is not disclosed by law, but we'd imagine it would awfully expensive and difficult to even listen to such vast quantities of data, let alone analyze it intelligently. They mostly listen for keywords now--bits that don't make sense (and thus might be code), certain red-flag words (like, well, "bomb," which seems kind of unsubtle but I guess we're talking about terrorists here and of course it's possible there are intricacies of language that are missing in translation), and any conversation between principals like bin Laden. Still, next time you're aghast at how much space the entire series of Blue Planet takes on your hard drive, just be glad you're not the NSA.