I also think that a research effort with the ability to process 100% of Tweets can most likely afford to pay Processing 100% of all tweets is not actually very

I also think that a research effort with the ability to process 100% of Tweets can most likely afford to pay Processing 100% of all tweets is not actually very hard or expensive: 2000 messages/sec is small potatoes if you want to do it in realtime, and even easier if you are just doing batch analysis queries. You could do it (with reasonable performance) for much, much less than $360,000/year (let alone 2x or 3x that for the 100% feed).