Hi
Whereas in a Builders clean, everything gets clean, kitchen cupboards, bathrooms etc etc, on a post plaster clean....or pre paint clean, all you will have is an empty shell and you are cleaning all the builders dirt etc away to enable the painters to come in and paint in a relatively dust free enviroment.
I would emagine that this would cost around 40% of the price of a builders clean as an estimate.
Obviously when you come to do and price up the builders clean, you will have already done some of the work.......windows and flooring etc
Regards
Tim