Hi Marc...
I've found that a fair price for a 2012 12C with 5k miles is about 56% of MSRP. Subtract $1/mile over 5k. And add $4000/12 mos of remaining warranty. This will give you a fair number to negotiate with.
For my car, the MSRP was $268,000. McLaren SF had it listed at $165,000. It had 5400 miles and 18 mos of warranty remaining. It was CPO. I got it for $150,000 + tax/title which was about $6000 under that formula above.
$150,000 for a 5k mile car with some warranty is about right provided the car has decent option packages.
The 12C is absolutely amazing to drive!
Hope that helps...
Good luck...
Ron