This is from Coinbase support:
"We don't charge a fee to send bitcoin out from your bitcoin wallet on any amount over 0.0001 BTC.
(Sending over 0.0001 bitcoin is free) The TX fee paid to the bitcoin miners is paid for you by Coinbase
If you send less than 0.0001 BTC, then there will be a mandatory TX fee added to pay the bitcoin miners. We won't pay the bitcoin TX fee when you send less than 0.0001 BTC.
Sending bitcoin from one Coinbase wallet to another Coinbase wallet is always free (no fee) no matter how little bitcoin you send.
There is no fee for receiving bitcoin."
RE: Is there such a thing as a "best buy" calculator for calculating the cheapest route from fiat to a certain altcoin?