i dont get the whole taxation per kilo thing, but i believe a w124 with a 3.2L m104 should weigh somewhere around 1500kg's, so that should cost around 800 euros (like the w210) in roadtaxes.

you mentioned that the w201 with 1.8L was fun to drive. if i were you, i would definitely be on the look out for a 3.2 M104 attached to a 5 speed manual, i bet that that would be real fun to drive.

good luck