In the Song Dynasty, the metal money was mainly copper coins (also called "consistent thousand characters"), and some iron coins were also used in some areas (mainly in Bashu area, because iron coins were of small value and heavy, so it was not convenient to carry, so the earliest paper money was invented in Bashu area later: Jiaozi). As for the conversion into RMB, it's hard to say, because the comparison between the two requires an equivalent, such as salt, iron, rice and meat, which are relatively high in value because of the low productivity of the Song Dynasty. But the house, wood, fur and medicinal materials are much cheaper than we are now. For example, how many tons of rice can be exchanged for wild ginseng at that time. Now, if you want to exchange rice for wild ginseng, you should at least change the quantity unit of rice into wagons.