Stay far far away from this car...
A year ago, our SL500 was parked and a heavy storm came through causing the water to pile up in the parking area. There was a bad rubber floor drain in the driver's side, which let a small amount of water in. Just to replace the carpet, padding, insulation, seat control module, and the few wires that got wet, as well as the bad floor drain (so it wouldn't happen again) was over $3k.
And that was MINOR damage, the only thing that happened was the drivers' side floor got wet. If the whole car was flooded bad enough to result in a salvage situation, I can't imagine what problems are lurking in there.