Adding to what Mikkel said: That first sentence threw me for a loop. I've stared at it for a good thirty minutes and still can't decide if it's wrong or right. However I think it's incorrect due to the fact it's a mix of the past tense and a phrase that deals with the future. I could be wrong though. "Would" implies a definite thing. So if the cost of the dam 'would rise' it means it will occur no matter what, /if/ you do a certain thing. "Could" is the conditional form of 'can' - if something 'could' happen, it means that it is a possibility, but know one can be sure it will happen. This is how I would say what you wrote: 1. "...the original cost of the dam was estimated at $25 billion, but by the time it is completed this could rise to $75 billion or more." 2. "...the original cost of the dam was estimated at $25 billion, but by the time it is completed this will have risen to $75 billion or more."

I don’t understand why you think “By the end of this year I could/would have saved some money.” is ungrammatical. It seems fine to me. I don’t understand your thoughts about lack of if-clause and “imply a condition” etc, so I can’t say anything about that. About "...the original cost of the dam was estimated at $25 billion, but by the time it is completed this would have risen to $75 billion or more.": I would say that it depends on the context whether or not you can say that. Without knowing the context I can’t tell you if you can say it. But I can’t see how you can change “could” to “would” without also having changed the meaning. “Could” seems to mean “might” in this context. I don’t see how “would” can ever mean “might”.