I have a Colt 9x23 that I used as the basis for a switch barrel 9x19/9x23 custom. Colt made about 1500 of these, and they sat on shelves for years. The round, while having great performance, is relatively unknown, the guns were nothing special, and they sold like snails run: slowly if ever. Colt resorted to dumping them with extra 9x19 and/or .38 Super barrels.
Mine was over four years old when I bought it, and it had been marked down quite a few times to help it move. The dealer was so happy it sold (well below his asking price) that he threw in every 9x19 and .38 Super colt magazine he had (well over twenty magazines).
I would value the Colt frame and slide like a regular 9x19 (since it is). The only 9x23 markings were on the blue plastic box and barrel hood. The other oddity is the recoil spring guide is unusual as it has polymer sandwiched inside of it. I would think $400 to $450 is a good price, especially if the 9x23 barrel is trashed.