Check this mentioned in Admin Guide.. I am not sure about the cost. I think concurrent license will be cheaper and many people can use. i might be wrong.
New users are created as named users.
New user accounts are configured to use named user licenses.
Named user licenses are associated with specific users and allow
people to access the system based on their user name and
password. This provides named users with access to the system
regardless of how many other people are connected. You must
have a named user license available for each user account created
using this option
• New users are created as concurrent users.
New user accounts are configured to use concurrent user licenses.
Concurrent licenses specify the number of people who can connect
to BusinessObjects Enterprise at the same time. This type of
licensing is very flexible because a small concurrent license can
support a large user base. For example, depending on how often
and how long users access BusinessObjects Enterprise, a 100
user concurrent license could support 250, 500, or 700 users.