Comment by johntash

Another thread mentioned something like a 30day unlimited trial. That could be a good way to gather metrics on how many searches/day to expect from users, and should help with pricing.

Which part of the service actually costs you more money? Is it the cpu/bandwidth of returning search results, or is it the indexing that happens before then, or the storage/memory?

Maybe instead of charging per # of queries, you could charge per number of sites the user follows/searches? You could always leave something in the ToS about abuse to have an option to stop users who are making an excessive number of searches.