Only by common sense deduction. To answer your question thoroughly,
I'd have to research the sums spent and sit down with an commercial
expert in civil engineering to see what would have been a sensible,
realistic cost of the infrastructure work.

Essentially my contention is based on three items: the figures quoted by
Tfl as the project costs; the amount of necessary, unavoidable civil
engineering and the amount of essential, routine railway work such as
new signalling and track installation. TfL quoted figures in the high hundred
millions. I seem to recall a figure of £ 800 million. This is unimaginably high for
a project where the only new section of route was a few hundred yards in Shoreditch.

In a properly managed and costed project, the three really big items of expense are the
land, the labour costs and the finance costs. I don't know what deal TfL made to be
allowed to build a new railway across Bishopsgate Goods Yard but it cannot have cost
hundreds of millions of pounds. Apart from that short stretch, the new bridge across
Shoreditch High Street and a very short new spur, the route already existed so the
land costs should not have been especially high. The labour costs also cannot have been
astronomical. Let's do some crude, back-of-an-envelope calculations. Suppose the
project lasts 150 weeks - it shouldn't have taken that long; suppose on average 100
men are working at any time - slightly unrealistic; and suppose on average their
employment costs are £1000.00 a week each - pretty unlikely: Labour costs = £15 million.
As interest rates have been extremely low for the past few years, the finance costs
should have been quite low too. So the three largest items of expense together can
not come anywhere near the hundreds of millions of pounds TfL said this project cost.
So where did the rest of the money go? New rail track, ballast, signals and cables
etc for just a few miles should not cost a vast amount so we are left with the flyover
at New Cross Gate, the service facilities, two replacement bridges in Kingsland
and four new stations.

I have no idea how much was spent on Dalston Junction, Haggerston, Hoxton and
Shoreditch High Street nor how much they should have cost. Current costs of
building a three bedroom house with normal fixtures and fittings is about £125.000
plus the cost of the land. How much would four stations, two of them very simple,
on land already owned cost to build? How much did that service area near
New Cross cost? We know that the Emirates Stadium cost Arsenal £390 million
in a properly managed project. With that sum they bought an enormous chunk
of land in inner London and built a vast, state of the art sports arena. Does
anyone imagine that a train servicing depot on land already owned should cost
a similar sum?

I don't know what the flyover at New Cross Gate cost. If you held a gun to
my head and demanded that I guess, I'd say it should have cost about £10 million.

All the indications are that the costs of the ELL project rose to unjustifiable levels.