I think 10-15 GB would be plenty...
Well in MM there were many folders in my iDisk, but outsiders could only see the Public one... something like that.
Okay, I've had some time to mess with DropBox. Like JD mentioned, the Public sharing feature of MobileMe was the one useful feature. I haven't seen a way in either DropBox or Network Solutions to make a Public folder without making who accesses it register. They can download separate files without registering if you give them the link to the file(s), but can't view the whole folder. There is a workaround like I mentioned above by setting up one dummy email address for a Shared folder and giving the link and log in info to the students, but there is the total file size limit.
With DropBox you get 2 G free, but you would need to pay $10 a month to get 50G. Then you'd need to pay a web host to host the web site too, that would be separate.
If you used FTP to share files through Network Solutions they would be hosting your site for you, $10 a month, and you could use your 300G of disk space for your files without incurring the extra charge.
With FTP they could use a web browser and see the whole folder so they can pick and choose files, it would look like this;ftp://gesplus.com
User name - student_files
Password - $tudenT
You can name the folder/user whatever you want of course, that's just one I set up to show you how it works. It is set as read only so files can't be deleted or renamed if one uses an FTP client instead of a web browser.