When I first priced the car last August it was MSRP + 10. In October it was MSRP + 5. By December it was MSRP. By June we were hearing about MSRP - 6. Plot that and you get about the same kind of curve that is being experienced in the UK. DC did a similar pricing scheme when they introduced the Viper and the Cruiser. Not a big surprise.
The time to evaluate the cost of ownership is before the purchase. If you didn't, shame on you. If you did and your number turned out wrong then it looks like you need to rework your algorithm.
Go buy a SLK. Drive it off the lot. Be surprised when it depreciates 15%. Get cranky. Hop on the SLK website and spread some sunshine there.