I don't doubt that sort of figure for such a short stretch of track, but....if what RB says here is correct...
It does make you wonder when the complete Borders Railway reinstatement was
...Network Rail agreed to build the line by mid-2015 for £294 million,
The line comprises 40 miles (65 km) of single-line track over a distance of 31 miles (50 km), plus 42 new bridges, 95 refurbished bridges and two refurbished tunnels, and required 1.5 million tonnes of earth to be moved.[50][51][52] Stations are provided at Stow, Galashiels, Tweedbank, Newtongrange, Shawfair, Eskbank and Gorebridge.[39]
....
Amongst the line's 27 substantial structures, the greatest engineering challenge was posed by the point where the track met the Edinburgh City Bypass. At that point, a tunnel had to be constructed under the A720 road while it had been temporarily diverted; in total, the project incorporated five new associated road schemes.[50][55] Major challenges were also posed by abandoned mine shafts to the north of the route, some of which dated to the 16th century and had not been mapped.[50] More than 200 bridges were involved in the scheme, as the route crosses the Gala Water and River Tweed nineteen times.[45][55] One of the most vital bridges on the line carries the track over Hardengreen roundabout on the A7, and required extensive works throughout 2013.[56] Other works included digging out an infilled cutting on the outskirts of Galashiels and reconstructing a nearby bridge to allow the line to pass under power lines.
Now that's 7 stations built and 40 miles of track and all for £294 million.
See that would make a lot more sense. This is what I found on
wikipedia, just reviewing Kirkby Station:
As part of the second Merseyside Local Transport Plan (covering expansion of public transport in the region from 2006 to 2011), plans were drawn up for the possible future expansion of the electrified line beyond the existing station. Since the existing track at Kirkby station makes interchange difficult, part of the expansion involves the construction of a new station in the Northwood area of the town.
This new facility, at Headbolt Lane - previously planned in the early 1970s but never built - would provide "turn-back" platforms for both diesel and electric services (likely in an island platform configuration). Exploratory technical assessments have already been carried out and Merseytravel have aspirations to construct the station as part of the Liverpool City Region Long Term Rail Strategy published in 2014.[6]
As of 2017, Merseytravel and Lancashire County Council have committed £5 million to a study into the opening of a station at Headbolt Lane and also in Skelmersdale. The plan would cost an estimated £300 million and would take a decade to deliver.[7]The study alone is costing £5m.
That’s just for a siding with a speed limit of five mph. I can’t imagine the costs involved for mainline. Plus the amount of work they’d have to undertake with ground conditions etc. I wouldn’t believe a word network rail say. Add to that the absolutely crazy money their staff are on.
Well if you take the Lime Street upgrade as a benchmark, that's costing £340m. That's to upgrade 10 platforms, making them longer and straighter, replacing a WW2 era signalling system, new track, foundations, drainage, improved electrics and overhauling the line electrification.
Plus - and I'm only guessing here - roughly 8 platforms' worth of track, probably extending anything up to a mile beyond the station approach (Platforms 1, 2 and 7 already have new track, as do the new platforms 8 and 9, although the old platform 9 - presumably will now be platform 10 - is probably having its track upgraded.)
And bear in mind, technically speaking Merseyrail
isn't mainline. It shares very little of its track with the rest of the national rail network. Merseyrail is about as close as a privately run railway gets to being nationalised: track maintenance is in-house, and not handled by Network Rail; and the new trains will be owned by Merseyrail and leased to the operator. Extending the line to a town that doesn't even have a railway station shouldn't really be an issue unless it's a complete scratch build.