Does anyone plan to buy extended centOS 7 support through TuxCare or similar service.
Me personally no.
I have no ideas about others.
If you do please let us know about your experiences.
I am hoping to be able to continue on PHP 5 for an intranet system
You aren't going to like me saying it but.....
Some things you just need to get over, and PHP 5 is one of them.
If you don't face up to reality today you will have to some time fairly soon.
You should have already planned your migration to newer versions already.
You are delaying the inevitable. Even on extended support its life will end before too long, so you are better biting the bullet and moving ASAP.
We have supported PHP 7.x and PHP 8.x for some long time to help people migrate because we have all known for 10 years this time would come.
You should be ready.
Remember also - you may buy support for the underlying CentOS itself, but there will be no support for anything SME related beyond assistance with upgrading.
Sad news, but no less true.