Hi KRISK,
Another solution which might be a great fit to deliver what you require is something called the E-Tiering appliance from NEC/NetApp
The product basically works to creates what the developers call stubs ( similar to a shortcut ) and essentially you can set policies to tier data based on how much data is actually being used and hence is the exact solution for what you want from a technical capability perspective
You can find more details in the two below links
www.e-tiering cloudappliance.com
www.necapp.com
The cost will depend on how much data you have but I am almost certain this could be the best way ahead from a technical and cost perspective in all probability
I ll say try and then decide for yourself
Drop me a line if you need further information
Cheers,
Bino