When we were young, impecunious, struggling to afford our first mortgage, and starting to have children (much more costly than cars and still are now, over 40years on!) We "invested" (what a travesty of the word "invest"!) In a very second hand Ford Anglia from a back street garage in Acton. A few months later she developed a big end knock (should have seen the light there and then) so me and a couple of pals lifted the engine out by hand, standing on beer crates - the old very solid wooden ones - with a big baulk of timber and some ropes (can't really believe we did that?) And I rebuilt it on the flat's kitchen table. Mrs Jock was much more tolerant in those days!
Mrs Jock, who is not from a "car obsessed" background, suggested I should keep a detailed record of what it was all costing and I then continued to keep a record of general running costs. A year later she, the Anglia that is, had to go for her MOT. Sold to me with a years MOT of course! Failed, of course, didn't it! (Notice she's now become an it!) Lots of problems but the most memorable was the sills which were completely rotten, stuffed with newspapers and skimmed over with glass fibre and filler (the garage called it "Mick". Never heard it called that anywhere else, must be a London word). Anyway we scrapped her and, having looked at the incriminating evidence of expense recorded in my book and being fearful of Mrs Jock's wrath, I also scrapped, lost that is, the record book! A few weeks later I bought a 1966 Triumph Vittesse! (There's absolutely no hope for me!) The early one with the 1600 six cylinder engine and the very lively handling characteristics produced by the swing axle rear suspension (have a read about Ralph Nader's "unsafe at any speed" condemnation of the Chevy Corvair for more on swing axle suspension and the "interesting" handling it bestows). Actually lasted us for a few years and sold on at a good price because it was a 1600 and not the more common 2 litre.
l have never attempted to keep a record of any sort related to the cost of running my many vehicles since. I do however go to considerable leangths to source quality parts at the most reasonable prices I can achieve and, of course my labour costs are pretty much zero. We run on supermarket fuel with Archoil 6900-P max additive (Mrs Jock collects the Morrisons vouchers but doesn't know I use the additive!) - Oh dear! Have I just started an additive debate? - From time to time, and always on long journeys (Edinburgh/Devon and Edinburgh/Salisbury are the two main ones) I keep a brim to brim fuel MPG check just out of interest really.
On reflection I'm really glad I don't keep records as I think if I were to know how much I've spent over the years I would immediately expire from heart failure and grief! The above is not to say though that I religiously keep detailed service and repair records in a card file in the garage along with any interesting technical data I come across which might relate to family vehicles.