If the money is Trump's private money, and if he has it earmarked for his campaign, then the ridiculously high bond requirement just adds to the overwhelming evidence that the prosecution, decision and penalty are all political and malicious in origin and are in various violations of the Constitution.
If the money is the campaign's money and of he is being prosecuted by his campaign opponent for political reason's then he has the ethical right to use that money for any legal expenses.
And as a bonus point I will add, if the NYS superior court is denying any consideration of a stay pending appeal, pending a ridiculously high unconstitutional bond payment requirement, then Trump has every constitutional right to petition SCOTUS.
I think you are conflating how you think things should be with how things actually are.
Since Trump was sued for things related to his business and not related to his campaign, it would be probably be illegal for the campaign to pay his legal expenses, even though there is an obvious political motivation to the case.
In order to appeal to SCOTUS, Trump will first have to exhaust his appeals through the NYS appeals courts. It is doubtful SCOTUS would short-circuit the process on a case like this, if it is even possible.
Understand, I agree that this is a political case and the facts of the case and the size of the award make it very likely Trump will get at least some relief if not an outright reversal. Unfortunately, the way the system is structured, that process will take time and money, and there may not be any way to speed up the process.