Those bastards.....they almost always default to a "new motor"as the fix. I've read it on forums all too often. Sorry, man, really. I would be completely shitty about it too.
Crank arm, Im guessing, is the same as the crank shaft which is deep in the engine. My suggestion is to call all the local machine shops within your radius and find one that does rebuilds. I found one close to me so if ever I need to (hopefully never) I've got a spot.
The reality is the 1st and 2nd "gen", as I've heard them called, 3.6 is a work in progress engine. I'll never buy another vehicle that utilizes it.
Worst case / best case, you can trade it in with the current market and still get a premium. I would suggest Vroom or CarMax and the like because they dont play games and their process is quick.
Keep us posted with what you decide and I wish you a good outcome.