I'm certain you know enough to stay away from early w140's, so by default, it's the w126.

Which one? You are more likely to find a good 300SE in your price range than a v8 model. You probably would be more familiar with the engine in this model than the M116/117 engines. I always thought the 300SE was the most "Euro" of the w126 models, due to the inline-six and shorter wheelbase.

Try for a 1990-1991 (dual airbags).