I’m in the process of doing this. I got a skip and its amazing what the neighbours want to get rid of. I dug out a load of earth that went in the skip. A neighbour donated some slabby rocks (not perfectly flat but ok) which I’m going to use in place of concrete. I’ve also buried a load of old rubble / stones that neighbours / I don’t want. I’ll then top it off with hardcore and mortar the slabs on this. Around this I’ll fill with 10mm gravel and keep a soil ‘island’ in the middle which I’ll plant with grasses and alpines.
With regards to settling, when you consider what some people park on, the recommended specs are overkill IMO. Sure if you regularly park your VW Amarok on the drive you’ll need a good base, but a lot of cars are regularly paked on lawns with no reinforcement (think campsite) or old concrete drives on a crumby 40mm foundation of stone (I think mine is) through to gravel laid on soil.
If you look on ebay you can get the plastic reinforcing mats for about £60 to cover an area for one car, but you’ll need to dig out 40mm depth of turf and then re-seed. I don’t think they look very good if the grass is cut really short.