Replacing Dropbox with: Amazon S3 + SSL + GPG/TrueCrypt + Mounting on OSX ??

Problem

So, right now we're using Dropbox to share various data files around between approximately 10 Mac OS X systems. However, we already have an S3 account and everyone on the lowest Dropbox plan of $10/month seems too expensive. We'd like to avoid any kind of local storage (share a disk on a desktop or…