$0.90 USD these days.
It costs $0.98 to ship a standard letter from the US to New Zealand.
For a standard letter up to 50 g - $1.45 AUD see: http://auspost.com.au/
It depends on which country you are in and how big your envelope is. The bigger the envelope the more stamps you have to put on. ( that's in the UK)
1.50