Unfortunately the C4 market is WAY down and will be for some time. It's a showcar and you'd have to find someone interested in purchasing one without wanting to build it themselves (rare). Due to it being moddified, I'd call it in the 15K-18K and even at that price I think it'd take quite a while to move it. For reference, bone stock, very low mileage 96 Grand Sports are going for 15K-18K and it's highly desired as a collectors car. You can even get a 1990-95 ZR-1 for under 20K now. All this makes your type of car a very hard sell.
With all this said, I'd list it somewhere like the
Dupont Registry and list it in the $20-$23K range. You might get lucky, but I'd think you'd at least be infront of the correct audience that'd buy your car. Good luck.