This was a demonstration I did for one of my real world clients. I scanned two faces of eminent personalities and joined the top of one with the bottom of the other. The angles of both the faces on the photos were at nearly the same horizontal and vertical angles, which is a must for edits like this one.

An edit like this would cost US$ 50 and would be complete in about a week. 
I would need the following:

1) Clear samples of the two faces in about 5 x 7 inches. (Bigger the better)

2) The faces to be at the same vertical and horizontal angles.

3) Specific instructions indicating which sample the final edit should be biased towards; the first or second.

4) Instructions about how the faces should be merged. E.g. the first picture above the nose and second below the nose. Please note that I may not be able to follow your instructions to the letter, but will follow them generally.