http://revach.net/article.php?id=4379

Section: Moadim   Category: Around The Year
Parsha Shkalim: Chizkuni - Haman Pays Enough Shkalim To Buy The Bnei Yisroel Fifty Times Over
The gemara in Megila (13b) says that Hashem gave the mitzva of Shkalim to ward off the affect of the Shkalim that Haman would give to Achashveirosh.  Tosfos says that Haman gave Achashveirosh 10,000 Kikar Kesef, which is equal to the half shekel of the 600,000 Jews that left Mitzrayim.  

How does the math work out if half a shekel for 600,000 Jews is 300,000 Shekel Haman's 10,000 Kikar is the equivalent of 15 million shekel (A Kikar is 60 Mana and a Mana is 25 Shekel).  It seems that Haman gave 25 time the amount of Shkalim that Bnei Yisroel gave.

The Shnayim Mikra brings from the Chizkuni that since a person lives 70 years, if you start giving at the age of 20 for the next fifty years you will give a total of 25 Shekel.  Haman did not only pay for a yearly Machatzis HaShekel, he paid a lifetime's worth for every single Jew.