Replacing Google GeoCoding for another solution

Hi there,

Situation
We are running a website where you can find office space for rent. On the homepage, we use a Google autocomplete search field where the user can enter the city name where he wants to search. We then show all available offices, sorted by showing the nearest offices first.

Issue
Unfortunately, we are now making way too many calls to the Google GeoCoding API and it is getting too expensive, even with little traffic.

Solution
We are looking for an alternative way to show the offices (search results) the same way, but with a lower number of calls to the API. For example: if we store the GPS coordinates of all offices in our local DB, would it be possible to make these calculations without using the Google API? That is what we are looking for. Or if you have another briliant way, we are open to suggestions.

The site is a WordPress website with custom post types etc. etc.