Keep in mind that for Europeans, Costa is the Carnival of cruise lines (literally). That is a typical price for a 4-day Carnival cruise. This Costa cruise is meant to appeal to local Europeans, not Americans who want to see Europe. It's a fine line, but realize you will not really see venice or Athens unless you book a hotel before and after the cruise.
The port stops appeal to locals - not to Americans, there is nothing of cultural significance in Corfu or Bari, Italy. Dubrovnik is the only worthwhile port on the trip.
This cruise is designed for Germans & French who want to sit by the pool and get a tan.