导购口语:

This is sale price. We earn very little in this line of goods.
这是最低价了，这类货品的利润很低。
We are practically giving this away. It's almost the cost price.
我们简直是在把这送人了。这差不多是成本价了。
This is the rock bottom price and any further reduction is out of the question.
这是最低价格，无法进一步降价。

语句解析:

This is the rock bottom price…这个是最低价格……
the rock bottom price = the lowest price 最低价，如果对方还不相信，你可以在补充道：You get a chance like this only once in a blue moon.（这可是千载难逢的机会啊。）我们都没见过这样的月亮，按照天文学家的说法，月亮不可能是蓝色的，至少这也是千载难逢的天象。所以once in a blue moon意思就是“千载难逢”。

情景再现:

This is our rock-bottom price; we can't afford to make more reduction.
这是我们的最低价了，不能再降了。
We can't come down any more. But you'll get a free gift if you spend up to two hundred yuan.
我们不能再减了，但是如果消费满200元，您就可以得到一个赠品。