All I can add is the PhotoGenic mask is pretty much the way to go in this area, thought I don't know about using one for a cosplay.
Having worn one a times, the following things come to mind.
The skin color doesn't usually match your own unless you buy a neck form from Natori .. this is really easily evident when in person (on my gallery photos I've photoshopped the colors).
The sight perception is extremely limited. To the point of needing a handler to keep you from running into things. Natori has an eye style that is much easier to see out of, but the eyes look less realistic.
These things cost right at $1000 and I don't think he is taking orders at the present time (if you went with photogenic mask).
On the positive side, looking in the mirror is like looking at a different person, they are form fitting to the eyes and cheek ,. and you sometimes end up sounding like darth vader because you end up breathing through the eye pinholes and such.