再看吧 is more like the English "We'll see how it goes". Which is not as strong as indicating certain disagreement, but can be used to mean that. Have a look at the two examples below:
有时间再看吧 - Let's look at it (the situation) again when we have time or I'll think about it later.
This is can be used in English to politely decline something, that is, you are deferring it indefinitely.
明天再看吧 - Let's reassess / have another look at the situation tomorrow.
You see in this situation, although you are saying you will think about it later, you have set a definite time. Far from being a certain disagreement. I guess it is certain disagreement for now, but not indefinitely.
考虑考虑 is similar to "Let me think about it". Again, depending on the situation, the same as in English, "Let me think about it" can also be used to defer someone indefinitely. This really depends on how it is said and how much trust you will have in the situation that this person will really get back to you.
If one of my friends asks me to do something difficult which involves things such as inconveniencing others, money or sacrificing personal time, but I am still willing to help but haven't worked out how I'm going to do it so it has minimal impact I will say something like "我考虑考虑,等一会儿再给你打" Let me think about it and I will give you a call back later.
As per your question above 让我想一想 is almost the same as using 考虑考虑, they both mean "Let me consider" or "Let me think about it".
So both of the above examples don't fit into the three points provided. They are more like being non-committal.
non-commitment: 让我想一想, 考虑考虑, 再看吧
dependent on outcome: 应该可以
not likely：有点难做， 应该是不行， 有可能做不到
not possible: 我是做不到， 不能做， 不行