什么是与Silverlight一起使用的基于云的文件存储平台？

I'm working on a Silverlight app that would allow a user to upload a few gigs of files to a hypothetical cloud based file store, then allow the user to view some data about those files later (more functionality than a file store). Ideally I'd like to use a free, per-user store such as SkyDrive but I can't seem to find an API for that service (and read elsewhere on stack overflow that programmatic access violates their TOS). Do any services fit this bill? I've heard of Amazon S3 but I understand that'll cost some money - is anything free?I'm working on a Silverlight app that would all