Your man maths aren't bad....
but even washing machine leased from vauxhall/citroen/peugeot/kia* et al (*delete where applicable) has to be maintained to manufacturers recommendations to comply with the lease, taxed and insured.
The largest additional cost (frankly ridiculous) after purchase, compared to the leased sh*tboxes is the road tax. However the lease cost for the white goods cars essentially is depreciation, which for the right ISF / GSF (and some RCF's) is glacial now at worst, and is the biggest cost in new and new(ish) car ownership.
So actually it'll probably be cheaper running and using the ISF, than the hoover with wheels, and if you look after the ISF there will always be a strong demand for the right car, in the right colour with good history, if you decide to move it on.
I look back and prior to the Lexus' I had, I ran a v10 M5 estate, as a daily, wonderful but flawed car. Drank like George Best out on a bender with Oliver Reed.
5 years old when I bought it. Even with it's insatiable thirst 13 mpg on the school run, a need for a BMW warranty at £150 per month (it did have £9000 of warranty claims in 2 years), and wallet shrinking servicing costs - it was cheaper to run per mile than the Merc e350 diesel estate, which was "bought" new that preceded it. Because it didn't depreciate, and it was a similar story with my ISF or GSF, and I know which I'd rather have.
Keep the ISF right and enjoy it as you say, life is far too short.