Have you seen the offers here?

http://www.drobo.com/offer/

Drobo + 4TB for $1,075 (£550). Now that is sounding better!

The other huge benefit of the Drobo is that as standard it isn't a NAS so you are connected to it directly via USB2 or firewire. This means small file transfer should not be an issue, and you have the share option if you did want to turn it into a NAS.