500 US dollars discount。

优惠的英文：discount

参考例句：

Domestic preference not applicable.

国内优惠不适用。

15% off with this flyer

凭此宣传品优惠15%

Application of preferential income tax rate, and exemption of income tax

适用优惠所得税税率，及所得税免除

For a group of 20 persons or above, room rent is lower (a special rate is available).

团体二十人以上，房价优惠。