I recently saw a finished & primer body just like yours go for $15K here in CA with a rebuilt 455 engine and all brand new suspension. Did not have a complete interior tho.
Hopefully, that helps you ballpark it.
http://www.TheFOAT.com/92GTA 1969 Pontiac Firebird w/BP 461ci stroker kit, 670 heads & XE274H cam. Primer black with black interior. 1992 Pontiac Trans Am GTA w/SLP Performance Package. Dark Jade Grey Metallic, grey leather, T-Tops.
