The Cloud Billing Catalog API offers programmatic access to all GCP pricing.

https://cloud.google.com/blog/products/gcp/introducing-cloud...

Re: pricing changes, I presume you're referring to the Distance Matrix API under Maps? That's rather separate from Cloud, but at the end of the day doing a lookup of all routes between M places and N places is going to cost Google M*N more than a single lookup.

Disclaimer: I work at GCP and used to work at Maps (but before the pricing change, which I was not involved in).