If you want to use Flat Rate and not show a cost at top, select "Other (see description)" for Shipping Service. That discloses no rates other than what you provide in the text description.
Calculated has the advantage for shipping methods that use weight, size/shape, and distance as cost criteria, like Parcel Post or Priority.
There is a shipping calculator at ebay, that can be of help to newbies.

http://payments.ebay.com/ws/eBayISAPI.dll?EmitSellerShippingCalculator
Danno