I bought a Princeton EO90 19" monitor just as 19" monitors were hitting the market. Think I paid around $860. Now you can buy a 19" monitor with similar or better specs for $300 so we can say 19" monitors cost roughly 35% what they did say, 4 years ago. The guy in the office next to mine bought a Viewsonic G810 21" monitor and says he paid $1200 for it. Today, you can find it new for $500, or 42% the original cost. So, if we assume these two monitors are "typical" of the trend, we can say that prices for 19" and 21" monitors have fallen at roughly the same rate.
Now I'm looking to upgrade to 21" since the EO90 is about to die. Currently can't decide between the Cornerstone P1750 or the Sony G520. They have very similar specs. The Sony goes for around $650 at the low end while the Cornerstone can be had for $590 from their online outlet store. In any case, both of these monitors are around 25% cheaper than the 19" EO90 was when I bought it.
arcas