It seems that monitors have gotten pretty cheap as of late. We can go to best buy some time and find one! After a search on some sites of stores that sell monitors, it looks like almost every monitor sold now is a widescreen, so it's going to take up more room on your desk. Fortunately, getting one that's 18-19 inches is pretty cheap and should give you a quality monitor (only 120-150 bucks for most of them!)
There is always the option of getting one online which could possibly be cheaper, but keep in mind that if they have any dead pixels that you want to get replaced you'll have to ship it back whereas with a store you can just drive down there and exchange it real fast.
Anyways, here's a few examples of cheap, good monitors at bestbuy:
Campaq 18.5"and
Acer 20"Both good choices for cheap!