I'm pretty sure you're already spending more than $2k per year already on your Subaru. If you're not, it's just another Subaru WRX waiting to hand-grenade at 180k kms, surely?
Is an estimate of $2k-2k5 concerning you because you don't currently have a clear understanding of what it costs to run a car year to year? Tax department says around 73c per km this year; I don't have the current AA costs though on previous history they'll be higher (fuel, rego, insurance, maintenance, depreciation). Yes, at 73c/km that's $7,300 a year based on 10,000 kms running, and most people say "what, how'd they get that?", 'cos they just pay rego, insurance and fuel without thinking about it, suck in their teeth when they get a repair bill, and never think about the cost of depreciation.
I think you'll find the BMW isn't a lot different to a high performance Subaru needing servicing, diff oils etc, and what about that cabbelt service and sparkplug replacement? They're costly on Subaru due to access issues.
Suggest you price the parts for an e60 550i: Retail on Air filter, oil filter, 2x cabin filters, 8 litres of longlife synthetic oil, a couple of hours labour. There's your annual service covered. Now add rego and insurance. Tyres are $1000-$1200 over two years (unless you've got staggered 19's). Add a $350 excess for one unexpected repair covered under MBI. $60 for an alignment, annually. And then add a margin for a service item or two with a couple of hours labour; perhaps it's your suspension end links, or a couple of coils and a set of plugs; these are once-in-100kms items. Might be the year you do the cooing system service, or the brake fluid replacement; each of these is every two years (it's smoother if they are staggered alternate years), they're not drastically expensive but they must be done.
Seriously, if that seems expensive, just make "The Sony decision" and buy the appropriate Toyota. That is, in the same way that buying a Sony product will generally get you a reasonable level of reliability and performance in any consumer electronics segment without needing to compare against anything else in the market, you're basically sorted with a Toyota.
As my mate says, in any given field: "if you play, you pay".
Hope that helps.