I had the flex disks replaced on my 300D and the whole bill was under $220.
You need to see a good indy mechanic. This job does not require any seriously special trools, other than hex allen sockets.
Eventually, the flex disk will break and the driveshaft will whack itself to death on the pavement and the pan of your car, but it will probably make a great deal of noise first. Clunking when you shift from Drive into Reverse, for example.
A flex disk could not possibly cost this much. Price one here and see.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"