If the money is Trump’s, then it doesn’t matter to the court if he has earmarked it for other uses - the fact that he has it means he can pay the bond, and undermines his request to have the bond lowered on the grounds of irreparable harm. If the money is the campaign’s, then it is irrelevant as to this issue, as I do not believe you can convert campaign funds to personal use. Since the judgment is against Trump and not against the campaign, using campaign funds for this purpose would probably violate campaign finance laws.
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.