Either the previous cleaner has walked or been dropped, or you're facing the old chestnut that they've been cleaned throughout the building process and only need a quick once over!!!!
For one off cleans we charge 1.5 times our rate for a standard initial clean.
Our quotations are usually based on drawings or occasionally site visits, so telling you a price here would serve no purpose. There really are too many variables.
Go take a look at the site and if possible the actual plots. Look closely at everything. Gloss and Mastic can be a pain and usually take longer than expected. "Kitchen worktops covered in dust" tell you that no protection has been in place so there maybe all sorts or trouble lurking. Windows are usually filthy and glass can't be properly checked for damage until cleaned, and then, depending on the developer you might end up having 'new' damage blamed on you.
If you work with the developer already have an open chat with him. Tell him it's new ground for you. Gain an understanding of his expectations and take things from there.