Need a file sharing solution

Hi All,

People in my paying membership want to share files with one another, and I don't have space on my web hosting for this (and I'm already on their largest hosting plan). So I'm looking round at other possibilities.

Ideally I need something that will...

- Create a single file-storage area
- Protect it with a single username/password (that I can change periodically and give out to members)
- Allow all holders of that username/password to upload and download (but not edit) files

It's important to ensure that only currently active members can get in - hence the need for a single login that I can change regularly. I don't want something that creates a whole separate list of members, so they have to create a separate account and I have to update membership of the group manually whenever someone joins or leaves.

And also important that members can upload files themselves, with no help from me.

I can either
a) use another site where I have a bit of space and find a script to install there in a password-protected directory
or
b) find a third-party service that does what I need

Any suggestions for either of these?

Thanks!