Microsoft are currently offering a free trial for their Azure storage and CDN service
You can find more details here - http://www.windowsazure.com/en-us/pricing/free-trial/
Remember you will be charged on any usage over this amount. You will be charged to the credit card you supply on sign up.
You can calculate possible future costs using their calculator. Just go to http://www.windowsazure.com/en-us/pricing/calculator/ and click on the Cloud Services button
