Honestly, though, private schools have it easier because (other than those schools that actually do focus on SEN as their raison d'etre) they mostly exclude difficult kids and kids with difficult parents. It's not like if you funded state schools to the same level they'd be able to get the same results!
My child's private school costs about 5.9 thousand a year for secondary (I am not in the UK, but am in a wealthy developed country where things cost about as much as they do in the UK). When a school does not have to deal with lots of social issues, you can actually offer decent education at quite reasonable prices!
Up to now, there has been little demand for affordable private education in the UK, because until the wheels started to fall off the cart, the general feeling was that "decent state schools are OK, so if you have a reasonable amount of money - but not a king's ransom - to put towards your child's education, you buy a house in the area of good state schools and get some tutoring in." Perhaps if the situation in state schools starts to deteriorate going forward, we will start to see more demand for affordable private schools that basically look like a nice well-functioning state school (similar facilities and class sizes, but everything works, there is a trained teacher for every subject, and minimal disruption). Or maybe not, due to COL and the need to put money into private pensions and offspring's housing deposits.
All in all, I'm starting to feel quite glad we made our future outside the UK, but do feel sorry for teachers and for decent, caring parents who do live there and are having to deal with these choices.