So investigated a little more on this car and came on to the polish forum.

http://forum.streetracing.pl/viewtopic.php?t=1879&postdays=0&postorder=asc&start=15

In it someone asks how much was spent. The person said he wasn't sure how much was spent but a guess would be around the same price of an S-Klass. also, it was mentioned that the owner wasn't able to purchase the stock wheels of the SLR because "it wasn't available at the store". The people who performed the work on the car also said that the work done to the car made it better structurally than the original.

edit: apparently its also for sale at 200,000 Euro.