Here is a price list for SLES ( SuSE Linux Enterprise Server) That will act as your Domain Controler, NIS, samba, LDAP, APACHE etc. server. From what you describe I would imagine you just need the licenced copy for $349.00
I believe the $15.00 thats listed for NLD is for a licence to add it to an extra computer for a boxed copy it is $50.00
I would say if you are really serious about it contact Novell, let them know the setup you need and have them get you a detailed price quote.