通过英文邮件的商务价格谈判中，老外压我价格，如何回应比较得体

Dear XXX(名字),

The previous quotation of $50.00 I gave you was the best price I can offer. Taking into consideration all costs and taxes, it is not possible for me to give any more reduction.

Thanks for your understanding.

Regards,

XXX(你的名字)

意思就是：

我之前给你的$50的报价是我能出的最好的价格了。考虑到成本和税，我不能再减价了。

谢谢你的理解。