Some rail construction costs in 1960s-70s West Germany, including U- and S-Bahns. Not everything is properly disaggregated by line, but many things are, including the core S-Bahn tunnels. The numbers for Munich are quite close to what one sees in broader media, filling me with confidence the other numbers are right as well. https://dserver.bundestag.de/btd/05/038/0503884.pdf