Just Acquired 2002 LT-A400F Eiger w/ Broke Crankshaft ... what am I in for?? What in the heck would've caused this??

 

ATVs often get really abused, hard to say why it failed. I think your best hope is finding a take out motor from someone parting out one. Maybe you could even use an Arctic Cat motor. My 2002 AC 400 has a similar Suzuki designed motor built in the USA. You might be better to part it out, put the money into a running ATV. Here is a picture of my $1,400 AC 400 in the foreground. You don't always have to spend a lot to get a good one.

 

You will struggle to get either a crank or a complete motor for less than the bike is worth when running. If you do manage to get another motor, part your old engine out, as engine/gearbox spares are expensive and hard to get. We had a 400KQ (same engine) that ran a cam bearing, and ended up getting the head machined and sleeved, as a new head & rocker box was so expensive and we couldn't find a used set.