iZimbra will be free though
Keep in mind that that's what the hosted providers make up for-
http://www.zimbra.com/partners/zimbra_hosting.html
Yes 3 user's is not very many; If you do want to contact zimbra sales-
Possible things to discuss in your request for a special price:
-no support cases
-they may be able to set smaller values for "MAPIConnectorAccountsLimit", "MobileSyncAccountsLimit", "ISyncAccountsLimit", etc and reduce cost
-maybe also turning off "AttachmentConversionEnabled", HierarchicalStorageManagementEnabled", even BackupEnabled"...