All this talk about monetary cost, what about the environmental cost? Do none of you care?
As already mentioned, the cost of reusing an existing car will be far more environmentally friendly than even cleanest new car.
But back to the original question, the finance of supercars is much harder nowadays as already said due to the reduction in appetite by lenders.
Generally I’d say (based on buying them in the past), if you cannot afford to buy the car twice then you can’t afford it.
If you get the right one at the right time they can be wonderful, I have broken even on Exiges, 911’s and 355’s, and made money on Vantages. But you can’t guarantee, and if it’s your main car you will be putting miles on it so value will go down. As a second car you don’t have to rely on an old exotic is great – but you will need to put aside 5k each year to keep it on the road (£1k service, £1.5k consumables, £1k insurance, £500 tax).
Hopefully you never need the slush fund so you will have spare cash and won’t need to put it all aside each year, but if you don’t put it aside you can bet you’ll need it.