Taxi Price: Khao San - Hua Lamphong Railway
I used a taxi to go from Khao San Road to the Hua Lamphon Railway station in Bangkok in November 2019.
I approached a taxi that had stopped on the Ratchadamnoen Klang Road (adjacent to Khao San, 2min on foot) and asked whether a meter is used. The answer was yes, so I got in.
The fare starts at 35 baht, traffic was not much of an issue, although a little waiting on traffic lights was involved.
At Hualamphon station the meter said 59. I gave 100 Thai baht and got 2x20 back.
In summary, the taxi costs between Khao San and Hualamphon are about 60฿.