All the comments above have made valid points related to IP geolocation APIs. There are already various free and paid IP-to-address APIs available in the market

All the comments above have made valid points related to IP geolocation APIs. There are already various free and paid IP-to-address APIs available in the market. Some are expensive because of the effort their team has put into continuously monitoring the accuracy of their service and keeping the data up-to-date. It is one thing to build an API layer on top of the free data sources and provide for low cost, but keeping the operation running with high up-time, improving data accuracy daily, adding new data sources and handling ambiguity with location data is quite challenging and requires a proper dedicated team. If you are a single person building this service, it can certainly take a toll on you. Nevertheless, there are many free APIs available which is just a wrapper on top of Maxmind's free data source. But if you can build a niche group of people who willingly pay to use your service, it is possible and as you mentioned be able to offset the running cost.