The reason that there is a discrepancy between advertised size and viewable area is that for CRT monitors (the big *** ones you'd be used to taking up all your desk space) is that part of the tube is actually behind the plastic edges of the monitor, so your losing part of your tube, diminishing your viewable area.
That problem doesn't exist for LCD screens, which can have their entire displayable area viewable.
The prices of CRT monitors have come down considerably in the last year or so, a 19" flat screen, high quality monitor would probbly be available for < $200 (flat out guess, since i'm going on australian prices * exchange rate).
Another thing to consider when buying an LCD is that you can get dead pixels in the display. Basically just one dot on the screen which wont update. If these appear in the first couple of months of ownsership take it back. They commonly appear in the later stages of an LCD's life but can occur at the start which means the hardware is defective.