How many CALs should the client buy?

[chieff]

Customer is specing a new Windows 2008 Standard Edition server to support 40 ACT! for Web users, no sync users, no local user - all Web.

Microsoft User licenses are expensive ($100 ea?) and if there's never more than 10-15 users logged in, can we buy 10-15 CALs?

Or is it even simpler than that ?  Can we get away with 1-2 since the ACT! Impersonator account is the only 'user'

btw, the server will not participate in Active Directory - customer doesn't even have a domain.