Westminster Palace repair costs

I've just read in today's i newspaper that the estimated cost of repairs to Westminster Palace is £3.5bn over 4-6 years if both houses of parliament are moved temporarily and £5.7bn over 32 years if the work is done while MPs and Lords remain on site.
To me, these costs sound absolutely extortionate. I mean I understand it is a large, complex building, and the work is no doubt complicated and intricate but still...
£3.5bn to me sounds exorbitant no matter how much work there is to be done. I really was extremely interested to see a detailed breakdown of the costs, so I looked online and found the 'Independent Options Appraisal' prepared by Deloitte LLP for Parliament. The document is 250 pages but nowhere in it could I find a simple list of works, materials, services, etc. and what they each cost. There was a rough list of the works to be carried out and a vague outline of the costs, in which you can see they have allowed huge amounts for 'Inflation' - at 3.6% which seems weird and 'Risk' and also shown the overall 'Construction' 'Construction Delivery' and 'Program Delivery' costs, but nowhere was there a direct list of items and what they cost...
No doubt it will be the taxpayer who is footing the bill for these so-called emergency repairs so I would say the public has every right to see an itemised quote. I simply cannot fathom how the costs can be so high and I think the government have a duty to show the public how they've reached this number and enlighten us on the tender process, if the works have even been put out to tender. For years I have been noticing the way that huge figures are thrown around when it comes to the reported costs of projects in the public sector, with little detail on the actual value for money that is being obtained and no insight as to whether the figures are actually accurate.
And don't forget that in this country we have a terrible record of public projects finishing well past the deadline and well over budget. Seeing the estimated costs for these repairs seriously makes me wonder if the people in charge are just taking the piss, lining themselves up for back-handers or some other way of profiting from the work.
The funniest thing to me is that we live in an outwardly capitalist society, where the attitude is to make money at all costs, and make more and more money progressively, to the point where a profitable year is not seen as a good year if the profits are less than last year's profits, and yet the government, the people in charge of the country, the people who are in many respects the ones we look to for advice and guidance, are so often seen to be completely off target financially, constantly overspending, frequently making budgeting mistakes and consistently failing to get value for money.