19" and 20" are not even comparable, prices should not be so close.
20" steps up to 1600x1200 (or 1680x1050) resolution, 19" are closer to 17".
Also, looks at the panel type (s-ips/ TN / etc) and of course response time,
inputs, pip, and other features. I'd go for the best $300 20" you can find,
Samsung and Dell make some great ones.
here you go.
and i have seen some of these panels for as low as $249 at other stores, ie costco, cc. the chimei was on sale at newegg for less than $300 last week. good luck.