There are a few ways buying discounted Apple product via Apple's official website.
If you are a university student, or teacher, or staff you can get the a new Mac at special price.
For Macbook Air, it is about 5% discount
For Macbook Pro, it is about 7-9% discount
For Mac mini, the discount is S$20
For iMac, the discount is about 5%
and For Mac Pro, the discount is about 7%
For those fan of Macbook Air, and other way to get discounted Macbook Air is buying through Deal.com.sg
If you are looking for even deeper discount, you may consider buying Apple's official refurbished product.