Who are you flying with?
If you are on Singapore Airlines they do great deals for stopovers. You get decent 2 1/2 or 3 star hotel for a song. It also included free shuttle van to and from the airport. Passing through customs and immigration is a breeze. After enduring US Customs and Immigration on many occasions I can tell you it was a delightful surprise how fast, efficent and friendly the staff where (the immigration offical even offered me a sweetie whilst she processed my passport). The roads are empty at that time of night and you would be able to take a cab into the downtown within 20 minutes.
Even if you are not on Singapore airlines I would still recommend checking out Expedia for hotel deals. They are quoting the Peninsula Excelsior Hotel where I staid as US$96 a night. I would assume you would be able to add a hotel shuttle as part of the booking process.