Guessing game for you...
As you may, or may not, know, they work by splitting the light from a bulb into three beams, shinging them through three different-coloured LCD filters and them re-combining the beams to form a full-colour image on the screen.
One of our projectors developed an odd blotch in the image, and a few minutes' furtle by our IT technician found that one of the LCD filters had packed up - the layers had delaminated slightly.
Cost of a brand-new projector - 465GBP.
Care to guess the price of a replacement LCD unit?