I typically use "NADA" for MSRP prices.
According to them, a 1985 300D had an MSRP of $31,940 - which is very close to Nates figures.

Here are some of the other 1985 Mercedes MSRP's.

190E - $23,430
190D - $23,510
300D - $31,940
300TD-T - $35,310 (wagon)
300SD - $39,500
380SE - $42,730 (what I currently own)
500SEL - $51,200
500SEC - $56,800
380SL - $43,820
300GD - $45,950