How is the living cost compared to the cost in Mountain View in San Francisco, CA?
Check the comparison from Numbeo: Cost of Living Comparison Between Hong Kong and San Francisco, CA.
You would need around 5,661.56$ (43,916.74HK$) in San Francisco, CA to maintain the same standard of life that you can have with 49,000.00HK$ in Hong Kong (assuming you rent in both cities). This calculation uses our Consumer Prices Including Rent Index.
The Cost of Living Index Rate is also interesting.