You sound so stressed out with this, I'm not in anyway surprised. I know how much time can be spent sorting out provision for SEN. It sometimes feels like my full time job!
If you have an EHCP you are quite a way along the line.
You have several options but only one or two will work if you cannot be at home.
Is there a school with a specialist SEMH unit attached? I'm guessing not as you'd have sourced this already.
Have you talked to your named co-ordinator and the LA? The name and contact should be on the EHCP.
Take control. Ask them to list all the provision including schools and attached units approved and in your area and what might be suitable. Ask also for the Alternative provision list.
It may be that your son could do his schooling for the time being in alternative provision. Our area has many different options for children needing more help, especially with SEMH needs.
For example, out of the 12 or so alternative providers there are three farms (we live rurally) who will provide either 1:1 or supervision in a small group. They do core subjects, life skills, cookery and animal management. They take all ages. The difference is they will find a way to adapt provision to fit your child rather than expecting your child to fit in.
You might have to look into a child minder to cover wrap around care, but transport is included for children up until 16. This could be to drop off and pick up from a child minder.
They should be able to tell you the band he's been awarded and whether it will cover alternative provision. It might be a case of visiting alternative providers ASAP and getting it before panel quickly to either get the next band agreed or to get the existing funding changed over to a new provider.
School obviously feel they can't cope, sadly years ago when there was more money in the school system schools could muster up funding for 1:1 in the classroom. This made all the difference. Now classes barely have funding for a teaching assistant or bare essentials like books.
Talk to the LA, I'm concerned that the school have said PRU for a child with SEMH needs. It may not be at all appropriate. Some PRUs are suitable and geared towards SEMH, some are not. Is there anyone in your locality you can ask?