It does depends on how you play/want to play the game indeed. With how updates are drip fed by PD (so far) and other games I want to play my plan is quite different - get all the cars and then just launch a GT7 for a few hours when I feel like, and check new updates whenever they are out.
I would skip on a few VGTs (don't like nearly all of them anyway) if I'd get all LCD cars before that, but at the current LCD's update pace I'll end up with all of those anyway.
Yes, it's a grind to do so right now, but I used to play old school MMORPGs where in some cases grinding for one level at the end game would take 20-50x time needed to get all the cars in GT7, so despite being quite older than I was back then (and not having as much free time), it's still doesn't feel as long/bad.
262.5m in total, but this does include some cars you get via cafe and via missions (like Chaparral 2J, current LCD's rally car for 2m and probably a few more), so it can be a bit less depending if you've got those or not.
I did some rough math and I need around 150m for the remaining LCD cars, mostly thanks to a few 18-20m cars (4 cars from Alfa, Ferrari, Porsche and McLaren alone being close to 80m). Few more expensive ones around 10m, and the rest are rather cheap.
Currently I have around 270m credits acquired in total, so for now going to buy the rest of regular cars and then just wait for the LCD to catch up. If it weren't for the 100m credits limit then I'd finish with grinding around next weekend since I usually play 5hrs/day and 4 of which is Tomahawk on Tokyo farm (can't be bothered to run remote play script and leave both PS5 and PC on at nights, so I do everything "manually").