KBB lists private party value using Excellent condition at $21k for the upper end. Considering Hagerty's just announced the collector value for the vehicle I think a premium will be required above the KBB pricing. $23k to $25k sounds reasonable to me given what you state and might still be considered a deal.
2009 G8 GXP, SRM, M6, Onyx, Roof. (#1818 of 1829) a.k.a Gianna
Show: Tint, VG Sharkfin, 6k HIDs + fogs, 20" TSW Interlagos.
Go: BMR, GForce, MGW, Monster Clutch, 3" SOLO, Dynotech, Squash DW255s, Tein, NLP Twin Turbo!
Stock: 363 whp/367 tq SAE (Dyno Jet) 13.149 @ 108.21 mph
Mods (older): 399 /399 SAE 12.711 @ 108.66 ,1.548 60'
Mods (old): 602/614 SAE 10 psi, 6* 11.33 @ 125.26
Mods (new): 600/631 SAE 10 psi, 10*