The fact that he has threatened divorce if you do not move with him to the East Coast is actually far more concerning to me than the question of whether or not you should move, his parents, or even the financial issue.
Someone who makes unilateral decisions (and yes, I know he discussed it with you prior to your marriage, but as you pointed out, it was always just a vague possibility, which is quite different) about really big, important things like where you live, and threatens to leave you if you do not comply is not a spouse I’d want for anyone. That’s not a partner, not a team player – that is a bully.
Whether his parents are ageing or not, the two of you should be making decisions like this together. When you get married, your own marriage and family comes first, and wherever possible, you try to come to a compromise with your spouse.
Your husband is making this very black and white, and personally, I have a big problem with black and white people. There are many compromises in this situation:
* He could move out there, and you could remain in CA whilst you find a job on the East Coast. You could visit each other back and forth during this time.
* If he wants to spend time with them, I don’t personally see why it’s necessary to move there. Is it not possible for him to visit them more often, or take some time off from work to spend solidly with them if their health is not good? I mean, after all, if he is working full-time, how much time is he really going to be able to spend with them? Is he planning to move into their house? To be there every evening?
* Alternatively, if money is not an issue, I see no reason why they can’t come up and spend time with you. They needn’t uproot their lives but can perhaps come and stay with you for a few weeks from time to time. Or, they could move to you if spending so much time with their son is so important to them. It is easier for them since they don’t work.
The way your husband and his parents are riding roughshod over you is really concerning, and from personal experience, it’s not a good idea to give in to bullies. Personally I’d probably tell him that I can’t move just yet – not for the foreseeable future and not before I’ve had time to think about it and found a job. And let the chips fall where they may.