Typically, any hi-res (1024x768 pixels and higher) LCD TV screens cost
2-3 times as much as an equivalent computer monitor. (Equivalent in
pixels and physical dimensions.) Even factoring in the cost of a
possible built-in tuner and A/V connections on the TV screens, the
price seems abnormally high. (This question doesn't really apply to
large TV screens 32"+, as computer monitors don't have an equivalent,
but as a good example, a 20"  1280x768 pixel LCD TV screen costs about
£500 compared to £200 for an identical computer monitor.) (or $
equivalent)

I would conjecture that more people are in the market for TVs than
monitors, but like I said, this is just speculation.

The TV versions usually cost more for several reasons.  
1) The TV versions have higher quality audio handling (sometimes even digital).
2) The graphics card is both highly complex (for all the different
ports) and is self contained.  A computer monitor doesnt have a
graphics card in the same way.  It uses the one thats in the computer
where the TV version has to recieve the video, translate it, then
display it.
3) The TV versions have to be HDCP compatible (HD copy protection)
otherwise it would not be able to play HDTV.  There are also several
other formats and copy protection things that they need to be
compatible with, all of which cost money for both the part cost + the
company getting the permission to make them.

-Hope this answers your question, Todd