does anybody know how much it costs to replace the clutch and flywheel,brake pads and rotors (stock brembo's) and timing belt on a 2003 G35 Coupe

 

i also need new syncros and a throw out bearing

 

There is no timing belt. The 3.5L engine has timing chain. As far as the rest of the items you mentioned, it all depends what you buy, where and who does the installation. If you go to the dealer, buy some industrial size Vaseline and lube up before they bend you over.

 

does the timing chain need to be adjusted or replaced

 

No, it does not. There is an oil pressure activated tensioner that constantly keeps pressure on the timing chain as long as the engine is running. It will usually outlast the life of the engine, unless if for some strange reason it breaks, but it is not likely that something like that would happen.