That is a somewhat high, but not out of line price. You may want to have it professionally inspected at a competant indpendent or dealership. Have it checked for accident damage and a thorough mechanical inspection. (where are you located? we may be able to recommend a good place in your area) There are about 1/10th as many 400E's as there are 6-cyl's. (and 1/10th as many 500E's as there were 400E's)
BTW, you will probably be getting new tires or tires and wheels soon after getting the car so figure that into the equation. The OEM tires were a bit inadequate for the power and curb weight of the car. In any case the 400E's are an excellent car. If you have anymore questions or whatnot let us know.