Yes, the 300E is a wonderful car, but consider that the list price of a base 300E in '86 was $34,700, and $2100 is on the low end of current asking prices, so don't set your expectation level too high. Based on the asking price, this car probably has a number of problems, due to deferred maintenance or repairs.
In particular, repairing a non-functional A/C system can cost about the asking price if the evaporator requires replacment, so you might be better off paying more for a car with everything functional.
Do a full functional check of all systems and ask for maintenance and repair history documentation, but don't hold your breath. Also inquire about the rate of oil consumption. Unfortunately this car might be one major repair away from car heaven.