[link|http://www.dyndns.org/|http://www.dyndns.org/] get a subdomain, get a client at [link|http://www.dyndns.org/services/dyndns/clients.html|http://www.dyndns.or...ndns/clients.html] and then run DirectUpdate or some other Dyndns client to change the subdomain to the DHCP IP every 5 minutes or less. The subdomain will be like boxley.dyndns.org or boxley.homelinux.com where boxley is the subdomain name that they registered. Run this on one machine to be the server, and then set up a SFTP server on that machine. Hard Drive space is cheap, cheaper than paying a hoster if you need 10 gigs. Make sure that you lock down whatever machine will get assigned the subdomain to, because it is going to be on the Internet. Put it behind a firewall and then lock out all ports except for the ones you need. Of course I think you already know how to do that.

For a SFTP server, consider this one:
[link|http://winscp.sourceforge.net/eng/index.php|http://winscp.source...net/eng/index.php]

But there are others out there, I think Cygwin has one built in or available for it. [link|http://www.cygwin.com/|http://www.cygwin.com/]

Edit: Fixed typo on Cygwin URL