Depends on your arrival time. During regular hours S$25, around midnight S$35. Plenty of taxis available when you exit the arrival hall.
Casey.

As you quickly figured out, your travel agent will charge you many times what it will cost you in Singapore. The taxi lines are neat and orderly and the service is very fast. It's no hassle at all to get a taxi when you get there.

Forget about getting the transfers from your travel agent. Once you get out of baggage collection/customers look for the signs leading to the taxi queues. There's a regular one and a limousine one (Mercedes Benz cars are used generally).

limousine
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Travel Fare/Destination (From Airport to City)

http://www.changi.airport.com.sg/


* S$35.00 (flat rate)
* Airport to any destination in Singapore
* Surcharge of S$10.00 is applied for each extra stop enroute to the final destination.

Regular taxi
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Travel Fare/Destination (From Airport to City)

* Approx. S$16.00 - S$24.00 (excluding surcharges)
* Midnight surcharge: 50% of metered fare (midnight - 6am)
* Airport surcharge:
o S$5.00 Fri-Sun (5pm to midnight)
o S$3.00 all other times


To get back to the airport you can just stop one and pay the metered fare with a small airport surchage (unless you like to ride in luxury of course).

If you want to save you, the MRT is available. Costs less than £1. Must travel light though.