Is it possible to upgrade to 3 phase after handover

Hi all,

My builder just quoted me $5000 to upgrade to 3 phase for our currently constructed house in Melbourne. That's from the street to the house (less than 10 metres). He said it's going to cost more later.

I plan to do it after hand over before I lay down the concrete. Is it really going to cost more to do it later?

Thanks

Sounds expensive, check with other electricians, would think about half or less.