Cars of similar complexity will cost similar amounts of money to fix. In my experience BMW's parts pricing generally isn't any higher than GM's for comparable stuff (though don't even THINK about pricing an M5's S62 engine, complete...) and parts for some Fords are ridiculous ($1000 Taurus C-pillar window, anyone?) if you can even get them (they're starting to obsolete stuff 5-7 years out of production.)
The LS6 in the CTS-V isn't too costly (LS6 crate motors are, what, $7500?) and the T56 transmission is becoming a commodity but those Brembo calipers certainly aren't cheap.