there's a money changer in suntec (near where the duck tour is) that is always busy with long queue. i had a look at their rates and it is very close to the interbank rate (for buying SGD). if you are buying 20k worth of SGD, i am sure you can chat to the money changer for a better rate than rate they are showing on the board.
now, is the free meal for me or for you???
