Ultimately you're at an impasse aren't you?
What does he expect you to do? Pick some money off the money tree? Or, as you say, perhaps he wants you to get into debt. Very, very fair and reasonable of you not to want to do that!
The conversation ultimately doesn't make a huge amount of logical sense. He knows you don't have the money but he keeps showing you pics etc.
Given it doesn't make sense, I would step back and think about what's really being "said" here - what the "emotional content" of the conversation is, not the facts on the surface. And then try to talk about that.
Is he upset that you prioritised something else over a holiday - yes he agreed to it, but now he's actually experiencing it, he's feeling something. Perhaps he's feeling resentful that you prioritised something else over time together, which can easily turn into "you don't value our couple enough". I wonder if that's what he's feeling deep down. I don't think it's fair, but it would mean responding with things like, Time together matters to me, and I understand how much holidays matter to you, but ultimately I only have so much money and in this instance I had to prioritise X. And then, if my hunch is right, maybe you could find other ways to enjoy special time together that meet the same emotional need but that aren't a holiday.
I might not have the emotional content quite right - only you can really suss that out as you're there and you know him, but I'd recommend that approach at least, whatever underlying dynamic you identify.
I respect you not wanting to share what it is you spent the money on, but I think that might also give you a clue as to what the emotional content really is. If you spent it on something you did with friends, does he harbour a resentment that you focus too much on your friends and feels neglected vs that? If you spent it on a pet, similarly. I am not saying any of these concerns would be right or justified, to be clear. But I think it would help you to get to the bottom of what is really going on, since what is going on cannot be that your DH thinks you can magic money out of thin air if he shows you enough photos of holidays.