How to set shipping cost if cart subtotal is less than specific amount else free shipping?
This is applicable for all members even for not logged in users.
You can use Shopping Cart Price Rules to achieve this task. Open admin->promotions->shopping cart price rules. And you should add new rule (If you installed Magento with sample data there is must be shopping cart price rule named as "free shipping" and you can use this rule). See these reference to create free shipping rule: