If you go to their "packages" page[1] and select "premium", it gives you a table with "requests (per period)" and "month-to-month (price per period), and it is indeed "up to 100" for $99.00. For up to 500 tweets per request.
Seems pretty clear, though I can't fathom why they chose "periods" rather than "months". Crazy expensive.
It sure seems that way. If I understand their copy correctly this looks really really really expensive. I'm assuming the tweets per request is the limit to the result set returned, which is crazy small.
I mean, you've got to think someone has done an expected demand / price model and decided that this will maximize profits. Only people they need to justify to are shareholders.