It can vary:
Low serial numbers, from 00000001 to 00000100, are sought after, as well as palindromes (23599532), solids (with a digit that repeats eight times), seven-of-a-kinds (66666665), ladders (45678901) and important dates (12071941). … Right now, on [Dave] Undis’ website, you can buy a $1 bill with the serial number 00000002 for a whopping $2,500. If that sounds like chump change, consider that a $5 bill with the number 33333333 goes for $13,000.
(Hat tip: Cowen; Image from CoolSerialNumbers.com)
The Dish 