You may have missed during the summer the release of this very useful tool: the Microsoft Datacenter TCO Analysis Tool available for free at this location : http://www.datacentertcotool.com/
This tool will help you calculate the TCO (Total Cost of Ownership) of deploying a Microsoft Private Cloud vs. a VMware Private Cloud. The tool is very comprehensive and includes in the equation technical elements like the amount of Gb of storage per VM and non technical data like the salary of the full time employees
The analysis includes the cost of running systems in a public cloud offering like Windows Azure in the case you want or need to deploy a hybrid solution.
I can only encourage you to use this free tool and compare the results : http://www.datacentertcotool.com/
Enjoy building your cloud !