Man that sounds like a diasaster, didn't the car feel loose or weak?
these can be repaired but you need to find a welder who wont charge the earth for the work as this could cost you upto £500 depending on the amount of rust and dont forget once you start pealing off all the crap the damage will be even greater!
had the same thing on mine a few years back, funny enough that was a black car, and it required mega amounts but once it was all done the car felkt 10times stiffer or ridged!