You asked if it would have been cheaper to build a new ship vs rearrange an existing one, and there was already precedence for this. I suspect that there may have been pieces of the internal hull support structure and space frame still in place from the TOS E, but everything else, from the outer skin to the hallways, cabins, engines, shuttebay, etc., was changed. "This is almost entirely new Enterprise" said Capt. Decker. That was a completely true statement as far as I could tell. If anything, they went further with that E than they did with Archer's.