。。。是  。。。； 。。。倒是。。。；。。。倒是不。。。

这些语法有什么区别？

The difference between the former two is that '倒是' is usually used to emphasize the thing you are talking about; and '是' is just means 'is and yes' , sometimes people add some tones to emphasize.

 倒是不 can be divided into two parts: 倒是+不(another adjective), so it is similar to 倒是, just added another adjective with nagetive meaning by using '不'。

比如说：
贵是贵，但是我钱够了 (In fact, this sentence is just a colloquial Mandarin, and to make it a little bit standard, you could say '虽然它很贵，但是我的钱够了')。

"倒是"和"倒是不"好像有类似的使用，但是我不知道它们确定的用法。

请帮我！

谢谢

P.S. I think your Mandarin might be advanced enough, so that you want to know these nuanses of colloquial expressions. In reality, however, these expressions cannot be used in formal writings. 

In my conception:

倒是 is more likely to be "on the contrary" , "alternatively"

虽说大家都认为他表现的很好，我倒是不认为然

。。。是。。。； 。。。倒是。。。；。。。倒是不。。。

这些语法有什么区别？

比如说：
贵是贵，但是我钱够了

"倒是"和"倒是不"好像有类似的使用，但是我不知道它们确定的用法。

请帮我！

谢谢

“倒是”和“倒是不”后面一般会有转折，比如“时间倒是够，可是很麻烦”和“贵倒是不贵，但是我钱不够”；其实可以把“倒是不”这个结构和“倒是”归在一起，“贵倒是不贵”的意思是“不贵”，“贵倒是贵”和“贵是贵”的意思相同，是“贵”的意思，只是程度不同。

。。。是。。。； 。。。倒是。。。；。。。倒是不。。。

这些语法有什么区别？

比如说：
贵是贵，但是我钱够了

"倒是"和"倒是不"好像有类似的使用，但是我不知道它们确定的用法。

请帮我！

谢谢

贵是贵,但是我钱够了.

Literally:It is expensive,but my money is enough.   OR   Though it is expensive, i can afford it.

①:"倒是" is same with "是" in this structure. You can use one instead of another.

"贵倒是贵,但是我钱够了." is equivalent to the sentence above.

②:On the contrary, "倒是不" is negative.

example:贵倒是不贵,但是质量太差了.

It is not expensive, but the quality is too low.