Be careful with the "100 free searches" limit, it's not always really 100.
If you click the "More" button at the bottom of the search results page it reduces the number of free searches left.
In hindsight, it probably means they're re-running the search again with different parameters, thus "using" another free search.
However it's not at all obvious to the user that asking to display more results from an existing list would do this. :(
Frankly, it seems a bit dishonest to me. Which is unfortunate, as I otherwise liked Kagi.