I will be honest, a lot of money, but I don't bother trying to work it out to cost per mile, when they need work or a service it just gets done.
Had the Ferrari for nearly three years now, paid 152k, done over 12,000 miles in it. Servicing has been free (7yr service pack), but the last dealer visit cost me £700 in repairs and £2800 to extend warranty, its first major ownership bill, could be argued the warranty is pointless on a 458, but its peace of mind. MPG is probably terrible, insurance is £800 per year, tyres I've fitted one set in ownership so another £1000 and its latest bill is about £2500 to rectify some oxidisation issues and £3608 for a new windscreen which insurance will cover. Depreciation is unknown but trade offers are in the 115-130k region, retail would be 140-160k depending on dealer etc. In short for the marque its cost me very little as its held value well even though I have doubled the mileage.
Honda S2000 cost very little, service was £200, its appreciated by around £5000, insurance is £400, road tax is like £550.
Corvette, no tax, £150 to insure, only bills have been restoring certain parts, probably about £500 spent so far, no depreciation, its probably appreciating and last weekend it won best American car on show.
GR Yaris, new car, no depreciation due to times we live in, only cost so far was £350 for a running in service requested by myself, so all fluids change, insurance is £400. Tax I think is like £340.
Aston Martin, had over three years now, cost 42, now valued over 50k, was serviced recently and cost £650, insurance is around £550.
Porsche Boxster Spyder, newest purchase, paid 43k, probably won't depreciate and might appreciate due to rarity of the model, its new so has no cost so far apart from the mods I've done which are like £100. Tax is £340 and its £500 to insure.
The bulk of cost is insurance, road tax and fuel, plus servicing and maintenance. Depreciation fortunately is none existent as between them all they balance out and if the trend continues they will all be worth more than paid for.