Some estimated values, apparently the market has softened considerably.

GT 350 Fastback $70,000-75,000
GT 350 Convertible $100,000-120,000
GT 500 Fastback $75,000-85,000
GT 500 Convertible $120,000-130,000
GT 500 KR Fastback $85,000-92,000
GT 500 KR Convertible $180,000-190,000