I've just had a conversation with a solicitor who said costs for a fully contested set of proceedings to get a Child Arrangements Order would be between £75-90,000 if it went all the way to final hearing.
Are you in London by any chance? A lot of the central London firms quote figures that solicitors outside London simply don't recognise. When I was in practice, are used to reckon that you could add a nought to my bill if you used one of the major central London practices.
A good solicitor can be a huge benefit in adjusting expectations and introducing realism. They are invaluable for the haggling over details which form such a large part of reaching a final workable arrangement for the children. Oddly enough, I think they are less important in the courtroom itself, except for finding of fact and Final hearings. After all, a court hearing is just about two parents talking to an outside professional about how best the children are looked after. It's not a very technical business. A finding of fact hearing and some final hearings, however, are quite technical and a professional advocate makes a big difference.
That costs estimate is for an Armageddon situation.
The Family Court has a much more realistic outlook for timescale and attempts to conclude matters in around 18 weeks. Rarely does.
As part of this speedy process it is possible to go to a first hearing and end up with a final order by which each party is bound. This usually favour one party over the other hence it is better to try to agree matters between you (I know, it's easy for me to say).
I've seen Children Act cases reach the levels you have described but only after several years, many hearings and usually one very disturbed party who believes they know what is best for the child/ren despite input from experts who state the reverse.