Being from Minnesota, it looks to me like the bottom part of the frame (the lower channel) rusted off. That bend or channel provides a lot of rigidity to the frame so when that rusted away, that put more stress on what was left and thus the crack.
Insurance? Forget it. Why would insurance cover a rusted frame?
There is a youtube of a time lapse of a guy changing a frame on a pick up. Toyota? Or whatever one had the frame replacement issue. Bunch of rusted frames in a pile in back of the shop so the guy has quite a bit of experience. It is very very involved and at $80-120 an hour shop time, um what can I say? Forget it. Time to say bye bye.
Sorry to be blunt but would you rather be lied to?