That Mark I was made in 1979 according to the serial number you posted. Fair value I'd say would be $225 or less depending on the condition it's in and any extras you may get, like extra magazines. A 1979 model should have the A-100 frame so the same magazines that fit the Mark II should fit in it. The same goes for grips, the screw holes on an A-100 frame are the same as a mark II.