To put in into perspective, mine does 25k+ miles a year as my daily driver and the annual costs (rounded/rough numbers) are something like this (excluding petrol @ 27.5mpg average).
- Insurance: £800-£1200
- VED: £500
- Tyres: £600 (less than 1 set of Michelin PSS a year)
- Brakes: £400
- Scheduled servicing: £1000 (1 oil service and one inspection)
- Interim servicing: £400 (oil service every 7k miles or before 'Ring trips, plus brake fluid changes)
- BMW Insured Warranty: £1000 (fully comp, no excess, BMW assistance)
So, total of about £5k a year or £100 a week, or 20p per mile (if my sums are correct).
If I don't use the for some reason (i.e. working from home, or having to use public transport, planes, etc.) then my mileage can go down to 5k a year, so the servicing, tyres & brakes costs reduce significantly for that year, and could reduce my outgoings by £2k a year.
I've even considered renting a car for my 'Ring trips (i.e. flying/passengering over and renting a 'Ring racer). But whilst that might save me £500 a year in added maintenance (oil service, brake fluid change, wear on tyres/brakes), it would cost mush more to rent a car for the 6 days of track time (e.g. about £500 a day).
I bought mine at 2 years and 9k miles old - it's now 7 years and 84k miles old. Since then I know what's been done on it with regards maintenance, lorry accident repairs, paint correction details, etc. but I know the next owner will probably not think anything of the time & money I've spent keeping it in good running order.
Mine will be over 100k miles by the end of the year and I don't think it's worth keeping the warranty after that as the wear & tear conditions cover many more components.