Privately I would think mid teens. Compare kbb, Edmunds, and nada sites, add them up and divide to come up with an average. Also go on auto trader and look for similar ones.
'98 Dinan/RMS stage 2+(VAC cams, CES Cutring etc)
'15 Buick Regal "T"(wife)
'06 Saab 9-5 Combi 5mt (full suspension, LSD, clipped turbo etc)