Hello, I am working on a smartphone application that will require a backend web service - but I have absolutely clueless to how much it will cost.

Web Service will handle:
- login of users
- cataloging of our user base
- holding minimal profile information for users (the only binary data is a display picture which will be < 20k each)
- performing some very minor calculation/algorithm before return results
- All the above will be communicated to server from a smartphone (iPhone/BlackBerry/Android)

Bandwidth Requirements:
- We want to handle up to 10k users throughout the day.
- I predict 10k * 50 HTTP requests a day = 500,000 requests a day * 30 = 15 million requests a month

Space Requirements: - Data will be in SQL database.
- I predict 1MB/user * 10k = 10GB + overhead. In other words - space is not a big issue.

Software Requirements: (unless someone knows an alternative)
- Windows Server 2008 + IIS
- MSFT SQL Server

Note: This is 100% new to me, so please hit me with all you got. Do I need Windows Server or are there alternative? Is it better to get multiple cheap servers to distribute load? Will Amazon S3 work for me? How about Windows Azure?

Thank you!!