score:4
I did some reseach for you, and have found the following. As in the first reply to your question a page was linked, it listed some prices but not the prices you were looking for.
In South korean they have something like the T-Money Card, you can add funds on this card to travel with it.
But they also have something else called the MPASS,
MPASS, is a transportation card exclusively for international tourists traveling in the Seoul metropolitan area and Jeju. The pass offers 20 rides a day for the duration of the pass. Additional funds can be loaded to MPASS and be used as a Tmoney card.
The prices for these cards vary on depending on the duration you want to have the card, it can be a 1-day card up till a 7-day card. The prices also vary a bit, I will mention them here, and also provide a link to the webpage where I found this.
Card Duration Price Discounted price (after 17:00)
The MPASS, can be used in the following areas:
Seoul: subway lines, airport railroad all-stop train, mainline buses, branch buses, circulation buses, village buses, night buses
Jeju: Jeju city buses ※ Jeju pass can be used both in Jeju and in the Seoul metropolitan area.
The ticket can also be bought at several locations like the airport, and in Seoul itself. Incheon International Airport
Seoul
Source: http://english.visitkorea.or.kr/enu/TRP/TP_ENG_8_1_2.jsp