It’s quite amazing these days there’s enough free data and software available you can create such a tool on your own! How do you plan to make it pay the server costs though?
Mapping costs would be by far the biggest one. However, I'm very lucky that after the last big spike in traffic, Mapbox very generously admitted me to their community programme. You can read more about that here: https://trailrouter.com/blog/mapbox-community-programme/
The server costs are quite modest at the moment (under $200/mo), which I'm lucky enough to be able to self-fund through my other work. If usage were to massively increase then maybe I'd need to find a way recoup costs. But even all of the hits from HN have barely put a dent in the server utilisation, so there's plenty of headroom for the foreseeable future.