Here is their pricing information:
In theory, the benefit of Azure is that you pay for what you use, so you wouldn't need to pay much until your store was successful. In practice, the cost may be somewhat prohibitive for entry-level stores. For a baseline, single instance store, you would need:
~740 Compute Hours / month = ~$90
~1G storage = $~0.15
~SQL Azure Web (unless you have a very very large store) = $10
~Bandwidth between Azure and SQL = varies
~Bandwidth between Azure and users = varies
I'm _guessing_ about $120 a month, but the billing and monitoring features are not available yet, so I can't confirm. Definitely higher than typical shared hosting, but comparable to a dedicated server, and better than Amazon EC2 Windows.
At this point, for our customers, if the store is just starting out or is small, we would still advise using a shared hosting provider like Discount ASP. As business demands load balancing, high availability, geographic proximity, etc., move to Azure.
Another compelling option is the BizSpark program, which comes with ~750 free Azure hours /mo for 3 years, if you qualify:
At some point, I'd also like to look into writing providers that work against Azure table/blobs/queues. That would offer infinite storage at .15c/GB/mo instead of the 1GB limited SQL database at $10/GB/mo.
A third option would be to set up a multi-tenated solution, where multiple stores could be hosted on a single instance for a SaaS-type solution. I haven't looked to see if nopCommerce supports this.