OP, there is no happy outcome here because the decision has already been made in terms of moving house.
You are his parents and you can, obviously, simply tell him that circumstances have changed, and sometimes you make a promise that circumstances mean you can't keep. I have been in that situation with one of mine (nothing to do with schools). It wasn't a circumstance of my making that made me unable to keep the promise - it was something extraneous. She was in Year 8 at the time. She is now in Year 13 and it is still a bone of contention. There will be people on here who say she should put it behind her and move on (and when I'm feeling frustrated, I think the same). However, it continues to affect her. At some point, she will have to decide whether she wants to let it carry on affecting her forever, or whether she needs to/can find a way to draw a line under it. The latter is what she needs to do for her own future happiness and mental health, but it isn't easy. I feel guilty about it, and the breach of promise wasn't even directly of my making. Since then, I have always been very careful never to promise anything. I say things like "at the moment, there is no reason why X shouldn't be so, but I can't absolutely promise it.", or "I will do my best, but I can't promise it". There's no point in me promising anything as that particular bit of trust has gone.
Your son would probably be absolutely fine if he moved schools, assuming you can find him a place at a decent local one. Assuming he's reasonably sociable, he'd make friends and become involved with what's going on locally. It's nice of you to say he can still see his current friends every now and then, but their lives will quickly move on without him.
Whatever happens, though, some damage has been done to your relationship with him. Is there any way at all you could rent out your new house and use the money to rent something smaller closer to his current school? It could be until the end of Year 11 - loads of pupils move schools at that stage.
As for the way he's speaking to you: I know there are people on here whose children would never dream of answering back, but I would say that his response is pretty normal for a 13 year old who has found his world turned upside down.