I bought nearly the identical vehicle 3 months ago. See below the comparison of my vehicle to your friend's. MSRP new was ~$44,500 and at the time of purchase the CPO kelly bluebook value was around $39k but I was able to get it for $30,900. I also received an offer from another dealer i was shopping at with a vehicle containing nearly identical options for 31k. Based on the vehicles I looked at during my search and your options I would say a reasonable price would be $29-33k, but i definitely wouldn't pay over 33k, especially since it doesn't have the multimedia package ($2950 option), but with the options listed it is a very nice car and i imagine the dealer would let it go for the 30-33k range, although they might try to use the kelly bluebook value (which is probably 37-38k) to get as much as they can, but you should be able to get this car for the low 30s.
Goodluck.
Same options:
2009 C300 4Matic
Obsidian Black Metallic
P1 Package
6-Disc CD Changer
Different Options:
Luxury model
Multimedia Package
iPod Integration
No panoramic roof
15k mileage
MSRP: ~$44,500