I can't help with the estimate, but I'm very curious about why this needs replacing.
I expect that the only way that the cam and valvetrain would need replacing would be in the case of neglected oil changing over a long period of time, or low oil pressure. If these components need replacing, I would be surprised if the rest of the engine is not very tired.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in