The OP answered his own question:
How many houses have a large screen LCD TV - VS - How many houses have a pinball machine?
Manufacturing is plain and simple the volume of production. My guess is that these LCD panels being used for pinball DMD replacements are already costing around $20~30 maximum.
As others have said it is NOT the electronics making the high sell price but the time and effort required to make the product work for only a handful of buyers (when compared with the millions of TVs built).
