It appears that the action on the cassette decks and related parts has slowed in recent years - there was one point when your setup would have pulled an easy $1000 - working or not.
One of the biggest 'plus' factors for you is that the cassette unit itself is a console mount which is much less common than the various floor mount units. DIN cable is for a floor mount, and the microphone is a later, over-the-counter replacement. Originals had a straight cord vs. coiled, and a rather different appearance.
It appears that the faceplate of the unit is in good condition with no knobs missing and no cracks. Assuming that's the case, I'd say $5-600 in the current market. If it were mine I don't think I'd go below $500 for the setup unless it were a really good friend.