I would pay $50/Month to get real valuable leads on businesses/owner that are considering selling their online product based SAAS business.
- Opportunity Overload: http://opportunityoverload.com/
- FE International is a broker that does this: http://feinternational.com/
Also, I assume you'd want to be the exclusive recipient (or nearly the exclusive recipient) for these leads, because for most of the business brokers out there you can get a newsletter with the newest businesses for sale, though maybe not filtered as you'd like it.