I feel your pain. My '84 has bad rot in the rear rockers, but the rest of the car (mechanically and asthetically), is really great. These cars have hit rock-bottom as far as resale values go, so it is definitely not worth putting that kind of money into it. Just drive it as-is and enjoy it - don't stress yourself out trying to fix everything. In the mean time, look for a car with a nice body and interior that needs an engine or transmission. You see those advertised for real cheap sometimes.

GregS
'84 300D, 183k
'90 300CE, 173k