I'm not on Humira, but I am on Remicade. I've seen articles on the web in the past that the annual cost for Humira and Remicade are similar, but with Humira you don't have the added charges of the infusion. Of course, your insurance may look at the procedures differently when it comes to co-pays, too. Because mine is given in the doctor's infusion center, it's treated as an office visit and I have a $35 copay.
Some insurers won't cover Humira at all because it's not yet FDA approved for use with UC, so check with your insurance provider on that.
I know Centocor has a special program to help people through the first year of treatment and I suspect the maker of Humira has a similar program. You can find information about Centocor's program here:
Finally, if you live in a mid-size to large city, ask the doctor about local drug trials. If your wife could get into one of these, she'd have a shot at getting medication at no cost - although she could get the placebo for at least part of the time.