States with Economic Nexus - Resources?

I have mortgage broker client who gets most of his customers from internet advertising. He is licensed in about a dozen states but physically operates entirely from his home state and has no employees or agents. Every year I end up researching filing requirements for various states to keep on top of rules like California's 25% of revenue threshold for economic nexus. What is everybody else using to keep up with out of state filing requirements? I've looked at subscribing to BNA for this purpose but it was $$.

I use CheckPoint state and local. Also pricey. Most states have this sort of info available on their tax dept websites. Free.

Has anybody tried Taxbook's All States edition. Cheap at $89. Useful?

I use a multi-state specialist. She can address these issues faster and better than I. PM me if you want her contact info.