I know you weren't asking me, but i did over £30k miles across 4 years in mine and maintenance costs were very low considering 350+ bhp.
Water pump and cam cover gasket - doesn't matter which BMW you buy, you're not escaping those demons.
Total ownership cost (maintenance, servicing, repairs, depreciation) was little more than £200 per month.
Again, not asking me, but it would be fairly simple to work out a formula for a ratio of estimated purchase & maintenance costs to handling and performance. As a starting point to build from:
Value = ((handling score + performance score)×1000)/(purchase cost + (annual maintenance cost x 5))
Run some tests and tweak the multipliers if necessary to give sensible numbers. Might make more sense to estimate depreciation cost rather than total purchase price, and remove the annual maintenance cost multiplier.
Of course, for that to mean anything you'd have to devise some objective formulas based on objective numbers for all the costs and handling/performance scores