WantWhat you want is to apply a default destination to a new quote, so that Magento thinks it will be shipped there and thus show shipping costs to that location. Luckily there's a small extension that does just that: http://www.rapidcommerce.eu/blog/2012/04/allways-show-shipping-costs-in-magento/ (note the updated version, it's still working on newer versions of Magento even though it was released in '12).
You can find the settings in the configuration under Shipping Settings.