I can go from my local station to the CBD (2 stops, around 5 minutes) and it costs roughly US$0.60; another 5 stops on the same line to get to my favorite restaurant bumps the journey to about 12 minutes and costs me ~$0.90. Crossing the harbor from Hong Kong island to the Kowloon peninsula takes less time but actually costs more (almost $1.50) thanks to tunnel fees.
On a side note, public transit timing is one thing that has been irrevocably ruined for me by living in HK. On my usual travel routes the train frequency is typically 2-3 minutes and during rush hour it’s on the order of 30 seconds - the next train often enters the platform just as the last car of the previous train leaves. Granted it does shut for a few hours each night, but even the other top Asian metro systems can't match it.
When I used to spend a lot of time in NYC (before moving to Asia) I had no problem with the subways; now it’s a significant consideration for me when thinking about moving.