Jenna, I don't think the climb by itself may have been what happened here. Sometimes, road rubble can be kicked up (rocks and such) and if you are unlucky, and the chunk is big enough, you can end up with something cracked. The unfortunate think is you can go on driving for months or years before a hard failure alerts you that something is wrong. No question the steep climb taxes the system, but by itself, this wound not explain the crack. At 320, we can be sure some damage was done to MG2 and you most likely have a failure that requires the replacement. That being said, often transaxles can be had for less than half that price from a scrap yard. Get a few opinions from other servicers as to what they may charge for a used one. Sometimes dealers exclude that option, and other car shops think Prius owners are full of cash! Still, if you find the right shop, I would expect you may see that number cut in half.