prefab question

Does anyone have a ball park idea of cost per sq foot of one, minus land and minus foundation costs? Thinking of either two townhouses bet 1000 & 1400 sq feet. Or a 2 fam with units above one another. Or a 2 fam with units beside one another.
Does anyone know of a directory of prefab builders in New England?
Was in a friend's house yesterday with substantial structural issues and trying to push idea to just tear it down and get something new.

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