[prepend]

Dropbox, OneDrive, icloud, and others have a free tier that is completely sufficient for a password vault.

Their client used to support this and they stopped. Because their current way makes them more money.

Their old client was super easy for non-technical users and groups (just enter Dropbox credentials, etc).

[efreak]

Box.net supports webdav if that's what you want. I'm not aware of any other big name cloud storage providers that offer support for standard protocols. It's available for free accounts, too. This does mean the files aren't encrypted, however if your vault is encrypted that may not matter to you.