But Crossrail includes 8 underground stations, most with two entrances
(doubling many of the costs), the rebuilding of several miles of Great
Western Main Line including two grade-separated junctions (Heathrow
and Acton Yard), the electrification of 11 miles of GWML (requiring
the rebuilding of about ten bridges in Slough), rebuilding a of a fair
bit of GEML, rebuilding of ca. 30 stations (about half will be
completely demolished) and so on. It's a much larger project.

Yes, so they could reduce the costs by doing it at tube guage, and
having single entrances for the stations, and raising the level it
runs at through farringdon so that they can re-use the tracks for the
moorgate branch of thameslink.