Monetarizing a site with a constant stream of visitors is not easy. How many visitors will not access the free site anymore? How high are the expected revenues? Is the investment worthwhile at all?
The answer was clear after a short research: advertisements on the website are worth it. In the worst case, only the server costs are covered and in the best case you can invest in new applications.
And if you are already in the process of adapting the code, you can also change the map service directly.