If you download BES Express you will get 1 free license (CAL) and 2 extra would be $99 each. A way around that would be to sign up for BES Express 3 times and use all 3 CAL's and it won't cost you a thing
That might make getting the BES easier for ya and you will also get wireless syncing of your calendar/contacts/memos/tasks as well. The BIS solution will only get you wireless email.