A:Answer Depends on the model of iPhone you want to purchase, but you'd want to look at either Verizon iPhones at full price or unlocked iPhones (which are automatically full price). Verizon iPhones have the advantage of being unlocked for any GSM/UMTS/LTE carrier (including ATT and TMobile in the US), but with the ability to be used with the Verizon CDMA/LTE network in the United States; unlocked iPhones will likewise work with any GSM/UMTS/LTE carrier, but won't work with Verizon in the US.
You would then have to deal with import duty and customs.
Full-price iPhones start at $500 for the 8GB 5c and run all the way up to $1000 for the 128GB 6 Plus. Prices are in USD.
As far as getting the phone to Greece goes, you'd probably be better off to come over here and pick it up yourself.