There were pictures in the Telegraph article (14/3/22) that if there was a new stadium it would be built to the north west of the current position, so we could continue to play at OT without a problem, until the new stadium was finished, saving a fortune and reducing the build time. (I can't post pictures, maybe someone can.) This and the fact Spurs didn't own the land, is what jacked up their price. United own all the car parks north and south of the river and all the way down to the railway line. They also own and lease out the freight yard to the west of the car parks, on a short term lease. I think it's a 3 to 5 year lease and it's close to renewal. Possibly a reason why this has come up again or because of the Glazers PR spin away from the Superleague mess.
Buying the freight yard was done before the Glazers came in when United under David Gill when we were looking at updating the ground in the early 2000's and were struggling with Network Rail and came up with rebuilding as a Plan B. There are discussions about this on here both in the early 2000's, the early 2010's and in 2019, if you look back. It comes up when everyone gets board every 3-5 years and nothing happens under the Glazer's.
The womens/youth team stadium would be built on the OT current site possibly retaining the pitch or some of the historic features of Old Trafford and would be c20-40k seats or be easily expandable if only 20k.
Rebuilding is competitive in terms of price as redeveloping OT. Network Rail would charge us a fortune to close the line for rebuilding the south stand, even if it was for a few weeks. The longer it takes to redevelop, the more it would cost. There would be no income from the south stand while it was rebuilt. In addition there would also be reductions in match day revenue as you improve the north, east and west side to improve leg room, site lines and install the big TVs for VAR reviews, let alone sorting out the big issues of atmosphere and good WiFi in an old stadium. You could also gain revenue by what you add outside the ground for supporters instead of having car parks such as fan parks, an external museum, fan experience centre, separate concert venue, rides, big wheel, circus, any other crap for tourists etc as well as making it look prettier like a park and less like an industrial estate.