As for budgets, I've always said I have no idea where all that money goes.
The Network Rail electrification RUS (2009), which kick-started all this, gives figures for the costs of electrification schemes:
route (ie masts, wires) 25-35%
clearance (bridges, tunnels, stations) 30-40%
power supplies (grid connections, distribution) 25-35%
signalling (immunisation etc) 5-15%
specialised equipment (wiring train etc) 5-10%
So clearance and power supplies take up over half the budget, before you have put any wires up.
This unhelpfully doesn't break it down into materials and manpower.
My guess is the materials side is pretty fixed in cost, but the manpower side will be way out of expectation.
This being because the productivity of the project teams has been significantly lower than expected.
None of the above covers design and project management, where NR is directly involved and is the critical resource in getting schemes off the ground.
But to answer your question, most of the cost goes to NR's contractors and equipment suppliers.
The RUS said this about unit costs (page 30):
Electrification costs are usually summarised as a rate per single track kilometre and the report T633: Study on Further Electrification on the
UK Railway undertaken for the Department for Transport (DfT) by Atkins in 2007 quoted a range of rates from £500k to £650k.
This figure was used as a starting point for the RUS evaluations and further developed by comparison with current cost estimates, proof of concept studies into new delivery techniques and outline evaluation of route specific features.
This additional work has shown some opportunity for reducing the costs which could be realised during the detailed development of specific routes.
Whoever wrote that will now be squirming in his seat at the outcome.
Far from "opportunity for reducing costs" below £650k per stkm, we seem to be at a stratospheric £1m per stkm on current schemes.
NR has been due to publish a refresh of this RUS for some time, but we are still waiting.