I always buy the same type of car (4x4). So if someone else was buying something different, I'd look it up out of interest.
"I'm getting the new Chrysler Blah Blah next week"
I'd look it up firstly to know what it was, and generally have a nosey. I quite like cars, and all the different designs. I'd look at the price, not as the main priority, but to see if I thought it was good value for the buck.
If it turned out to be £80k, I'd be thinking, Christ that's a lot for that. And I might say to my friend, "I had no idea how expensive these are!" with no ulterior motive or judgement.
The only time I'd do something passive aggressively like your friend has, is if I was annoyed about the concept. For example, I have a friend always whining that she's too broke to do this, too broke to do that, can't pay your other friend back that £150, so sorry. She then booked herself a course of full body laser hair removal. And absolutely I looked the place up and saw even on offer it was £1.5k. And about two weeks later when we all met up next, and she was doing her "I'm so poor" when something to do with money was mentioned, I absolutely said "I hope you got the 50% off your laser course, that takes it down from £3000 to £1500, if you didn't, call them and see if they'll honour it". Purely because I wanted to call her out in front of our friend that she still owes £150 for some tickets too.
Nothing like this OP?
Also, I think it depends as well on the car. If you're getting a new mainstream car, then it doesn't come across as bragging. One of my friends got a new Gallardo and he hardly told anyone before hand, because it's almost impossible to announce you are buying a brand new Lambo, without it looking like bragging. I know that's a more extreme example, but the principle is there.