I need to calculate a lot of distances between several cities in Germany which are identified by a postal code, e.g. 10115 for Berlin. I cannot use the Google Maps Distance Matrix API because it would be way too expensive for the amount of requests (even with caching).
Does anybody know a self-hosted/offline API (maybe based on OSM?) where I can request a distance matrix/list of distances between cities identified by postal codes? Unfortunately, I couldn't find anything by Googling.