Remember seeing one on tinterweb some years ago, used a CD case as the flip up screen with a LCD screen flat underneath and software to flip the
display!!!
If you look on fleabay now there are quite a few hud kits that all look exactly the same ranging from 60 to around 100 quid - they use gps so could be
a handy back-up if a magnet or cable fails for your normal speedo....