On
http://www.blackberry.com is an offer for BES Express for smaller businesses who don't immediately need the full BES but would like to have the functionality.
There is an option to get one for up to 15 CAL's (this can be upgraded to a full BES server in the future plus other features) or 20 users (same features as the 15 CAL package). I am not in a BES yet but I keep up with everything related to BlackBerry LOL