Google did the terabyte slightly slower (68 seconds) on 4x fewer machines, but did the petabyte in 6 hours and 2 minutes (around 1/3 of the time of Hadoop) on nearly the same number of machines (4000).
If you are a company that needs to sort a petabyte once in a while and your data resides on the Amazon cloud, you could get 3600 high-cpu EC2 instances and do it for about $12k.
A petabyte is on the order of 100k bytes for every person on the planet. If you have that much data that you need to sort in less than a day, you can afford it.
Changes my figure quite a bit too. Up to $25K.