5. I am sorry that we are unable to make you an offer for the time being.
很抱歉目前我们不能报盘。
还能这样说：
We regret that the goods you inquire about are not available.
I am afraid it will be very difficult for you to get the offer now.
应用解析：
call into being 使产生，使出现，建立，成立；
come into being 产生，形成，成立；
in being 现存的，活着的

6. The offer is not workable.
报盘不可行。
还能这样说：
The offer is withdrawn.
The offer is given without engagement.
谚语：
Blood is thicker than water.
血浓于水。

7. The price drop greatly on account of large offerings from other source.
由于来自其他方面的大量报盘，价格已严重下跌。
还能这样说：
The price goes down badly, because there are many offerings from other source.
Large offerings from other source cause the price to go down.
应用解析：
a drop in the ocean 沧海一粟，九牛一毛；
at the drop of a hat 不拖延地；不迟疑地；
a drop in the bucket/ocean 沧海一粟；杯水车薪

8. This offer is subject to your reply reaching here before the end of this month.
该报盘以你方本月底前回复我方为有效。
还能这样说：
This offer is open when your reply reaches here before the end of this month.
This offer has come into effect since your reply reaches here before the end of this month.
应用解析：
or nearest offer 或略低于此价；可还价；
slight one's offer 轻视某人的建议