*** Good news! We added support for Open Street Map in the latest version!!
Simple Business Directory currently supports only Google map. But for 99% use cases, it is completely free. Once you add a billing account they will give you 200$ of credit every month – recurring which is usually more than sufficient for most websites. Please check this page for more details: https://cloud.google.com/maps-platform/pricing/sheet/
We do have plans for integrating with OpenStreetMap. But due to its lack of features compared to google map and other priorities, it may be a while before we can get to that.