Here are the prices in China. Since most options, such as automatic transmission, navigation etc, are preselected by the manufacturer we do not see the prices of most options directly. It is therefore easier to compare "actual" prices and rather impossible to compare base prices.
Just as an example, in China you cannot buy a 35i without the changer for 6 CDs or without the DCT transmission.
I have ranked the models according to their performance to price ratios. Since the SLK 55 AMG and 1-series 135i convertible are not sold in China, I do not know what their prices would have been here.
Interestingly the new non-S Boxter (with PDK and PASM) offers the best performance to price ratio.
Anyway, this table does not explain why Z4 sales is slow compared to other BMWs. It just shows how expensive roadsters are in general.