The earliest dispensers are quite rare and expensive. There are collectors books on Pez dispensers for those who want to know the value and dates of many of the Pez dispensers produced. The earliest Pez dispensers were not dated but if you find one without feet then it is safe to say it is a vintage dispenser. Pez dispensers didn't start adding the feet until the early 1980's.
Today Pez dispensers are very common, the more valued dispensers are from character themed movies. The newer Pez dispensers are more valuable if you have the original packaging but the older dispensers are valuable regardless.
Below is a picture of a Mexican Character Pez Dispenser which is worth about $100.
The featured lot of newer Pez dispensers below are relatively valueless, they are very common and there is no packaging. You'd get more for these guys at a garage sale at 25 cents a piece than you could by selling them in a lot on eBay.