Pretty sure I am not paying anything or using any API key :) Open Street Map basemap was too colorful and contrast with my color scheme was not very good in many parts of the map
If you're interested in switching over, feel free to shoot me an email and I can try to help!
Here are some demos [1][2] I've made without using any third-party map services. All open source! [3]
[1] https://wcedmisten.fyi/project/north-america-hospital-distan...
[2] https://wcedmisten.github.io/nextjs-protomap-demo/isochrone
It looks like you can just use OpenStreetMap instead, although the resources are donated so there is no guaranteed Service Level Agreement: https://operations.osmfoundation.org/policies/tiles/