The cost per search query is incredibly small. You could probably have <1% premium users. If your search engine is used by a billion people a day, 10 million paying users are still enough to pay a few thousand people developing your product (depending on your location).

I believe products can work that way, offer premium service and features for the very few that need it and a basic service to anyone else. In the end, the free tier is cheaper than what you'd have to spend on marketing otherwise.