St. Peter’s Fish is Tilapia 🙂 but it tastes good because they put lemon and some other spices in it. 
Plus of course, the fact that St. Peter’s Fish are from the Sea of Galilee and these are the fish that Jesus ate with his apostles and possibly performed the multiplication miracle with. 
In the area of Galilee and Tiberias, restaurants are scattered that serves St. Peter Fish. It costs around $15-$18. One restaurant I went to served the fish with fries, salad and  rice. This one on the photo is a bit of a downsized version.