I echo others thoughts on the PRU - I believe that you need to give it a go. I have heard excellent feedback from our local ones, both from students, and from staff. If he ends up doing well, then great, if he struggles there, for whatever reason, then it provides evidence for what hasn't worked, and for his needs. I know that a child shouldn't have to fail in order to receive appropriate support, but unfortunately this can be the case.
Is your DS working at the expected, or close to the expected, cognitive level?
Sadly the system for children with SEND only works for children who fit into the regular boxes. For those who don't, it can be a battle to get appropriate schooling. I would be cautious about wanting him to remain in his current school, although they have failed him, and have broken the law, IME it can take years for the culture and ethos of a school to change enough for them to be fully able to support children with SEND. Yes, they can eventually be forced to provide him with what he needs, but is that going to create the appropriate environment for your child, with staff who are fully on board with his needs and issues?
Have you asked about taking a sabbatical in the short term? This would give you some breathing space to think about long term decisions. I am a single parent to a child with complex disabilities, and gave up work nearly two years ago. It was the best decision i ever made. I was offered flexible hours, reduced hours, a sabbatical, but in the end leaving was the right decision for me. Not being able to look at holiday clubs, after school care etc makes it incredibly difficult. Long term, could either you or your DH do any kind of work from home? Can you downsize? I know that in an ideal world neither of you should have to be considering this, but it is the reality of the situation for SEND parents, sadly. Any decisions like this do not have to be forever, either, if he is settled and thriving somewhere, options may reopen.
I hope you can all find a way forward.