On and Offline Back Up Help!

I need a back up solution for our Legal department. They want to be able to access their pst files on the road as well as off the network. We use Sharepoint for document management so email is the most important right now. Its needs to involve as little thought as possible (automatic would be best) and it needs to be as cheap as possible. On-line is not an option they are very concerned about security.
Anything would be helpful! Thanks!