Is this considered rude?

yea, i think it is just a innocent question. same as when someone asks " is that car numbers matching?"
all on the same lines. i mean like, does itreally matter? well, it does if you have a for sale sign in the window, or have it listed for sale, but does not matter in normal everyday setting
i do ask people sometimes what they have into their ride. i do not think it is rude at all. i build these cars,a nd i like to see if i went over budget, or if i made out well. if i put 10k into a car, and see a comparable one that someone else put 35k into, then i feel good. or , if i am in the market for another project out of the norm, and i see one, i get a feel for what kind of investment i am looking at, to get my project to be comparable to the car i am asking about!