Thanks, Seth Williams I think this pay-per-search site that Karl James mentioned in that post, findtheseller.com, might be a good fit for my situation. I need a service that will look deeper than the last known address/phone number of the owner on record (since I already know those are no longer valid), and will search out the heirs and their contact info. Sounds like this site might do that, without having to sign up for a monthly subscription.
I hope to one day be able to justify a monthly subscription just for skip tracing services. 🙂