Filecoin is a decentralized storage incentivization protocol and is not intended to be a fully user- or web 2.0-developer facing platform at launch. We expect that ecosystem developers will probably build S3-like APIs and clients on top of the Filecoin protocol. They may also build or connect other popular blockchain tools like stable coins to improve usability and understandability of storage pricing or build in other features of user-friendly storage clients.
The Filecoin network has not launched so FIL does not exist yet. The price of 1 FIL will be determined by the market and may fluctuate over time. At launch there will also be components of the network that are basic and will undergo more development later on, such as the Retrieval Market (like a decentralized CDN). Another roadmap component is user-defined smart contracts that will enable use of the network to be programmable or bridged to other chains and networks.
Therefore direct comparison to Amazon S3 will take a while to be fully formed in terms of performance, pricing and usability characteristics. Moreover, Amazon has other storage products such as Glacier that could also be used for comparison.
Filecoin is going to be a really interesting attempt to decentralize cloud storage. I hope that any market comparisons to incumbent platforms are tempered by how hard the cloud model is to disrupt and how exciting and research-driven the Filecoin protocol is.