Hi,
In the settings of the prices, you have an "access level" setting if you have the Business edition so that you can display the prices only for logged in users with the "registered" user group.
Then, you can deactivate the "display add to cart button for free products" so that the products won't have an add to cart button when no prices are loaded for the current user.
Finally, you can use a translation override to change the text "free" that you'll get instead of the price and replace it with whatever you want :
www.hikashop.com/download/languages.html#modify