It all depends on how you block your shots. If they are wide shots, then you may get away with comping in real wings from stock photo sources. Are the shots close-up? You may want to look at how much it would cost to rent wings from a prop place and rig on set to how much it would cost in man-hours ($) to do 3D. Also, turbosquid has some decent models of wings for sale, as do other 3D model shops.
Todd Morgan
Creative Director
Freelance F/X Inc.