I did think about using LED type displays,not as big as the moving message shop displays,but it is an alternative. And as you say as its not for profit then it might be seen as a good opportunity for a manufacturer to do a good turn.
Basically its a minature CCD TV camera mounted to display a small area of a page onto a screen with an adjustable amount of magnification,the magnification being performed automagically by a cpld which runs a small video buffer and alters the tv out signal timing.It also does some contrast and edge enhancement.Normally similar devices sell for silly money.