http://www.blackarrowsoftware.com/store/prospero-x-3.html

At some point it's going to make sense to switch order to something like this - twice the hashing power at thousands of dollars less.  If you ordered this now, you would probably still come out ahead since you would:

1. Need to make up the cost difference
2. Be hashing twice as fast

1Th/s in March at $8000
2 Th/s in April at $6000

You would quickly make up for that month of not mining at 1 Th/s.