I have done some additional research and find out that it would be a very complex job to create a graphics driver for an USB connected display.
My intention is to connect such a display to an embedded Linux platform.
However I found something else that could be very interesting:
Dell offers a laptop with touch screen for 403,41 (including taxes ans shipping) and can even run Windows 7 (with some extra memory added).
See:
http://www1.euro.dell.com/nl/nl/bedrijv ... sdt1&s=bsd
A laptop can't be mounted on a wall, but by placing the parts in a new case/frame, it can be a very interesting solution... ?
Advantage is that a laptop keeps working during a temporary power loss, so this can be logged and be closed-down safely.