Sounds like a pretty expensive idea compared to a street directory to me!
From what I can gather you haven't moved here yet (I think you said early June in another thread) so maybe you haven't had a chance to look around too much.
Seriously if you are used to big cities then Singapore should be a breeze once you get used to the road system etc (doesn't take long) and a GPS is not really necessary. Also with the amount of roadworks they do here the GPS can get out of date pretty quickly.
There is an excellent on line street directory
http://./ and a couple of different paperback versions available at supemarkets/bookstores which list lots of places of interest etc etc. and these will get you anywhere you want if you can read a map.
If it is only to get you and the family around this island then I would recommend to forego the GPS and go with the books instead. Its a lot cheaper and even if you take a wrong turn here or there it doesn't take long to get back on track and sometimes you find things you never realised were there!
Have fun exploring!
