Once you set up a Windows Azure Virtual machine the costs incur on an hourly basis, but what if you don’t need the machine running 24 hours a day? What if you just need it once in a while for a few hours maybe? You might be tempted to just shut down the virtual machine from the management console but that doesn’t do anything: The costs still incur because the virtual machine is still reserved even though it is not running. See http://social.msdn.microsoft.com/Forums/en-US/WAVirtualMachinesforWindows/thread/1beea882-e05a-4e2c-9c1b-bfcad09b3e26.
In order to preserve the state of the virtual machine and reduce the cost you have to use the Windows Azure Powershell commandlets. The commandlets can be downloaded here from the Microsoft site. https://www.windowsazure.com/en-us/downloads/?fb=en-us They used to be on codeplex.
To get started with the PowerShell commandlets see: http://msdn.microsoft.com/en-us/library/windowsazure/jj554332.aspx
To begin working with your virtual machines using PowerShell see: http://msdn.microsoft.com/en-us/library/windowsazure/jj835084.aspx
The general idea is to export the state of your virtual machine and then delete it. When you need it again you import and start.