Frames are hard to come by. As you know, in this state, prior to the law changing several years back, thats the part that was destroyed by agencies. Inadvertently giving us all those "parts kits".
If I found a 4566 frame I would expect to pay $300+ depending on whether it was complete or stripped.
I think you would be better off finding a beater 4566 and getting the frame reconditioned. There is a Greensboro officer who has started bead blasting stainless guns - as an off duty hobby. Ive seen his work and it is nice. PM me if you find a beater and I'll put you in touch with him.
I always wanted a 4596. But I never saw one in person. I also didnt want the hooked trigger guard and didnt want to pay the scalpers prices for a 4596 that I saw online.
So, I took the top end off my 4516-3 and mounted it on an R4 4566 frame. Nice, well balanced pistol. But after awhile I simply preferred either the 4516-3 as it was, or the regular 4566.
Good luck with the quest!
Regards 18DAI