Yes, unfortunately, I had the same thing happen in Portland a couple months ago. Definitely made me question humanity for a couple days. Almost made me jump out of my seat when I started it up and was so loud. Our vans are an easy mark since you can almost sit under them and cut the cat out.
I was "lucky" enough that the thief cut inboard of the exhaust manifold and the muffler, so it was a fairly straight forward DIY job to replace. I called the Ford dealers and nobody could locate an OEM cat. I found one online, but like carringb said, it was super expensive. I ended up buying the only cat RockAuto sold for the van and it was about $350. Also had to buy the O2 sensor.
Link to cat here:
Note that this would have been covered under my comprehensive insurance, so check into that if you have it. Since the parts from RockAuto were fairly inexpensive and the job easy, I went ahead and did it instead of paying the deductible to get it done at a shop.
I planned on making a steel plate to block cat and deter the next thieves and then do a write-up here on the forum.
Good luck, and sorry to hear. It really is dis-heartening.