Extremely good advice.
It isn't difficult to spend £8k per year on something like an M5. You probably wouldn't want to buy a 2nd hand one that hasn't had that kind of love and care into it either.
Late last year I was browsing for a 2nd hand Nissan GT-R, a common theme with all the ones that are well-kept is indeed a lot of money is spent on them each year and it isn't difficult to spend £8k on such a car annually. Most of these cars especially where its owners state what they do to it on forums are keenly eyed by plenty and usually are sold before even an ad is published.
The 2 I did go view both had over £10k spent on it annually, which wasn't difficult to see why such amounts are spent on it.
4-8 sets of new tyres per year as 6000-8000 miles is the best you could get out of these tyres and many throw the tyres away as soon as 50% is worn, cost around £450-600 per piece depending on brand.
Front brakes are a yearly affair to change if ever you bring it to track, £800 per disc and £400-500 for a set of pads, some take pride that their brake pads are changed twice per year and generally don't wait till it is to the metal to replace it.
Full fluid change, engine oil, differential oil, gearbox fluids, brake fluid and coolant, for 10k miles a good one would have had one done twice per year with the engine oil replaced every 2500 miles. Full fluid change cost around £800 for a very standard quality one inclusive of filters. Labour rates are £70-90 per hour for good independent specialist places and 90% of all GT-Rs are sent to 3 of such specialist or Nissan dealers only.
Suspension parts don't last all that long either, many things start to go in as little as 15-20k miles some even less if you drive it aggressively, they don't come cheap and chances are you don't want the cheap stuff unless in reality you are simply not there yet
Didn't buy either that I was looking at though, 1 the owner changed his mind and decided to keep it while the other was asking a bit of a high price for it and wouldn't take a quid less despite it having a lot of miles but it sold hours after I saw it.
If it is a performance car then 10% of the price will go just for maintenance and upkeep. Fuel, insurance and taxes would be a separate budget.