Can anyone recommend a provider for either on premises Extranet software or alternatively a tried and true hosted solution?

Preferably something that you don't need to licence per user as we have clients coming and going that will use the service. 

This is for use in legal services and we are not interested in hosting data outside of NZ. 

Looks like owncloud could do it, but at a cost of US $9k per yet for 50 users (min) it's pretty spendy.