As time-consuming as it may be, getting information directly from prospects is still the best way to qualify them. Prospects will talk to you if you ask the right questions. But that takes time, and time is money especially in sales.
To save time, you'll want to find ways to question many prospects at the same time. Most customers like to be involved in the sales process from the beginning, and answering questions about their needs and preferences makes them feel like they are a part of the process. Direct mail surveys and quizzes invite response and garner qualifying information from lots of prospects at one time. Try sending out a questionnaire with a reply incentive to all of your unqualified prospects.