(though I don't recall the timeline well; that might have been a lie and he might have known he was dying at that point).

That is what I assumed. It was one of the first clues that something was up with him, and it snagged my attention. But yes, your underlying point about buying things with pain. I feel like this was something Green sorta had thought about, but only in a very surfacey way. See the ironic jokes about "cancer perks" -- the special things you get for being sick. He sort of engaged there, but not very deeply or very well.