Value of countermarked Korean 100 hwan coin

What is aprox. value of  countermarked Korean 100 hwan coin?

Here's a very good article on the entire hwan coin series:
http://www.dokdo-research.com/hwancoins.html

This seems to be the relevant section for you:

CiteerCoins like the one shown here, countermarked on their reverses with the Hangul letters, "견양" (kyeon yang), meaning "SPECIMEN," have seen much higher realized prices than those without it in the same condition.  These are the coins that the Krause Publications’ Standard Catalog of World Coins cites as “bank samples,” and states that “[q]uantities” of these coins “in uncirculated condition were countermarked… for distribution to government and banking agencies.”

I think you have an important rarity! Krause seems to give it a value of $100 - however, Krause is not always accurate. Still, very interesting.

A great find. Well done.

Thanks, nalaberong, great article, I also did some research and found one ended auction on ebay:
http://www.ebay.com/itm/Korea-south-100-Hwan-1959-C-S-Bank-Sample-Scarce-Issue-/390983007215?pt=US_World_Coins&hash=item5b08673bef

the winning bid $177 : )

most likely my coin will go for sale, because I am not collecting such a coins, It will allow to buy something really nice