There are big tech companies processing over 100 TBs a day. There are also game developers like Zynga that use Splunk for "big data" analytics. As far as cost, I am not sure what to say... contact your local sales guy;). We process 500 GB a day, but incrementally upgraded our license. I'd have to dig up the costs of each...
IMHO, Splunk crushes all of these solutions. While it is not "free", it has an incredibly short time to value. The first time I stood it up in production, it took less than two hours - most of our time was spent checking our work. Now, I can quickly analyze large volumes of data, and only have to manage a single software component. I love it!
Seriously irritating that they continue to dub this "network management". I have been in the network management business for over a decade, and not once have I throttled down anyone's network connection. That is a job for network engineers!