Instead of a motorcycle helmet, how about an old football helmet? Take off the grill from the front and you've got a helmet that extends to cover the back of the head and ears, but still has an open face, like Falcon's. Then, just worry about the visor and crest.
If you search on instructables, there's a tutorial on making a cardboard Boba Fett helmet. I think if you used the basic shape (cylinder with a dome on top) you could also go that route.