99% of web search providers today are using Google SERP scrapers, caching the results, and pocketing the difference when they get to return the cache from a hot query. It's not sustainable long term obviously. Anyone who actually has their own index would be able to charge <$1 for 1000 searches.

> What happens when the majority of searches are done by agents?

While I detest the idea, I don't think it's impossible for ads to appear in searches done by agents.