Sorry man.....
Frames are the foundation of a vehicle. I was fortunate. I knew about the frame recall on the Gen2. When I found this truck, I verified it had been thru the frame recall process. The frame was replaced in 2/2018, I bought it in 2/2020. Otherwise, I would've passed.
The "how much" question can only be answered by the buyer. Suggest advertising as normal, when a buyer comes to inspect, disclose the frame repair.
I understand the winter salt/brine impact. I'm an IA native.
Good Luck on the sale.