Much has been stated in the past few decades about the dangers of mercury and the chemical's use in thermometers. It is true that mercury can be a dangerous chemical, though there is some dispute about how dangerous it is if properly cleaned up.
As far as affordable thermometers go, the mercury thermometer is the most accurate and has several other advantages over alcohol-based thermometers.
http://www.ehow.com/list_6317976_advantages-mercury-thermometer.html