Well it's the old story of what someone will pay for it, but prices of these W124 series models in good running order are only going one way. I think this is partly because one has to be a real dog before it cannot be brought back to life at a reasonable cost, unlike many others.
Fair observation, but provided you can form a clear estimate of what's needed (i.e. minimal bodywork/welding) I prefer the cheaper buy which requires more work. I have lots of time and enjoy fettling my cars, so not for everyone, but this way you know exactly what's been done and it's to your standards, not those of some (possible) bodger who jsut wants to have an MOT and a runner to move on.