For FANUSJ - aah, now I see the difficulty: wasn't aware that most of your people are field staff. Anyway, sure looks like the VSAT option is the best, though this would depend on your costings...
Another thought - instead of downloading mail via POP3, why not instead host a mail facility with a web-based interface? You could do this either on your own server with secure access to the Internet, or on the ISP's facilities. Something like Postfix with Squirrelmail comes to mind (Open Source and no license costs), which would preclude the necessity for RAS, and also obviate all the hassles associated with mail clients, virii, etc. You should perhaps give this a bash first, then checkout the traffic - you may find that all of a sudden, there is no need to incur extra expense on an upgraded or new facility...