I found this old coin while cleaning out my backpack, and it got me wondering - how long could I have lived off of this coin for during the time of its introduction?
Doing some research indicated that the coin could possibly be a 2 mun denomination Sang Pyong Tong Bo coin from Korea in the late 1600s - but any further searching hasn't given me any indication of its value at the time of circulation.
I don't know the data for 1600s Korea, but we can look at the data for 17th century Jiangnan in China. This was a very rich region, so grain prices are probably lower than in Korea, but in 1638, the prince of one bushel of rice was 1.9 taels, so around two and a half ounces of silver. Each Chinese tael was supposed to be worth 1000 wen (or mun, in Korean terminology), so rounding, 2 wen would be about 1/1000th the price of a bushel of rice. However, as you can see in this table, after a spike in the mid 17th century, grain prices quickly dropped off, remaining in the general are of a tael a bushel until the 1730s or so, which would make a 2 wen coin worth about 1/500th a bushel of rice.