"Modern studies suggest that, on purchasing power parity basis, one tael of silver was worth about 4130 RMB (modern Chinese yuan) in the early Tang Dynasty, 206

"Modern studies suggest that, on purchasing power parity basis, one tael of silver was worth about 4130 RMB (modern Chinese yuan) in the early Tang Dynasty, 2065 RMB in the late Tang Dynasty, and 660.8 RMB in the mid Ming Dynasty[citation needed]." [1] So taking the nearest estimated value of a "tael", 100,000 taels of silver * 4130 CNY / 6 CNYUSD, the irrigation system costed around USD $68m in today's dollars to build, back during the Qin dynasty. There were an estimate of 20 million people living in Qin china.[2] By the time of the Han dynasty, just 200 years later, the population tripled to almost 60 million [3]. [1] https://en.wikipedia.org/wiki/Tael https://en.wikipedia.org/wiki/Tael [2] http://en.wikipedia.org/wiki/Qin_dynasty http://en.wikipedia.org/wiki/Qin_dynasty [3] http://en.wikipedia.org/wiki/Han_dynasty http://en.wikipedia.org/wiki/Han_dynasty