I'd love to make this work, Forrest - drop my name in a note to [email protected] and let's see if we can get you setup with the Isochrone plugin (https://blog.mapbox.com/add-isochrones-to-your-next-applicat...) which sits on top of the Mapbox Matrix API. https://blog.forrestthewoods.com/visualizing-commute-times-3... is awesome!
60 requests per minute is not very many.
Sadly I’m not sure any service will be able to do what I want at an affordable rate. :(