Full Cloud Storage Options to Replace Local Server

I have a very geographically-dispersed client that currently runs an in-house server at one location.  

The client is a marketing firm and the users tend to work on various projects on their respective computers and then upload the completed projects ( sometimes 100GB in size ) upon completion.

Their current storage runs close to 2TB.

Currently, only users in the main office access those shared files but that will be changing and users from across the country will need access.

I have searched for a few different options and can't locate a suitable solution.

Box.Com was reasonable, though they charge a fairly large fee for initial seeding.

Rackspace is a solid solution, but their pricing structure is based on storage + bandwidth; we are interested in a simple, not-changing fee structure ( ie., Rackspace cost would change every month depending on how much bandwidth was used ).

Any solutions would be much appreciated!