The reason that you can't see why refurbishing an old set would be cheaper than building a new set is likely because you have not built a new set. The bonus with building new is that you can do or have done a better job than the factory did. But rebuilding an old set should also give you the ability to end up with a better than factory set if you include some value added effort and materials such as Coytee mentioned. Best regards Moray James.
PS you can buy beater LaScala for 4 500 a pair a shop built set and cabinets will be at least 800 dollars and more if you use all baltic birch. Your choice.
:yes: With even 1" MDF running about $45 a sheet, building large speaker cabinets gets expensive fast.