This is a little off the point, but... I just saw something the other day - some funny article about what would happen if men wrote personal-advice columns. Some woman, I think, writes a letter about how her car made funny noises and stopped running, which meant she had to catch a bus home, which meant she arrived home early, which meant she caught her husband with another woman. She asked what to do. The male columnist replied with detailed information on how to fix the car.
Believe me, what happened at your house is not in any way unusual!
Look at it this way: On this site women post questions about a lot of things. Let's say a mama is posting about her experience of the night before, when her baby was running a temperature, she was concerned, and her MIL (one of those EVIL MILS!) shrugged it off. It's very likely that one answer will focus on the evil MIL, another will focus totally on the baby's temperature, and yet another will be about whether the mama worries too much.
You mentioned car repairs and... ZAP! That's where your husband's brain went! (Not only that - his brain went to the part where *action* was required - specifically, monetary action. Guys generally go for the action scenes!) He lost everything else because his brain stuck to that part of your conversation like a magnet. It's not just men. Women do this. I think everybody has brain-stick periodically.
You're right: your husband started thinking dollar signs and was getting upset about that. If you get upset with him now, he simply won't understand why, because you know what the financial situation is.
I don't know if this can really be overcome, but a little communication might help. Yes, I know, but it's worthwhile at least to try. Something like: "You know, Jim, I'm going to be scared to ask you anything about the car from now on. I thought I was doing the right thing being concerned about its acting up, but you took your frustration out on me. So if you'd rather find out these things yourself, just let me know and I'll keep quiet." If his brain goes off again about expenses, say calmly, "Well, then, you'd rather find out these things for yourself." If he says, "No, no, I need to know them," you can respond, "Well, then, please don't shoot the messenger." You say this calmly (you're on the same team, remember) and then you *go away* and give him a chance to process it (and save him from making the further mistake of answering, "Well, it's YOUR car!").
I've always had to struggle with this sort of thing because my husband and I have very opposite types of brains. These days, when I run into some problem like yours, I'll preface the conversation with, "Well, I'm just about to make your day a little brighter." Then he knows there's a problem coming up. If I'm upset about something and want some sympathy (rather than wanting something fixed), I'll ask, "Is your sympathy department open today? Because if it isn't, I'll keep my pity party to myself." I know it sounds dumb, but sometimes it's helpful to give a guy a clue right up front about what his brain needs to focus on.