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Architect should be able to work with you on a “value engineering “ exercise.
I did this recently - reduced some opening sizes (less steel) kept more of the existing building. And offered alternative layouts reducing the build area in m2 chunks showing the resulting impact on brief (ie client can’t have everything for less money so needs to compromise)
Needless to say they pretty much ended up back where they started.
People want what they want.
What your saying to me seems like you need to cut off quite substantial amounts and that might not be enough.
Doing work yourself can save large amount but it depends what you can do.