Ouch, I just found the transfer charges by digging a little deeper before returning to this thread.

My wife will be doing approx 66,000 miles with me in the next few months, which would cost US$1,830 to transfer.

It's a bit frustrating because those 66,000 miles would be quite useful added to my balance but they are not so useful on their own. I guess we can get at least a regional companion ticket at least. My wife only travels with me so I don't think there are any benefits to having her own MPC card either.