Ta dum! Here are our Monsters University costumes.
I made myself leg warmers and a skirt out of some purple fur I found on clearance. I just sewed tubes with elastic in a casing at the top. My PNK shirt was via Etsy. John's OK shirt was bought on Amazon, and I got his MU hat at Disneyland.
They even have matching trick-or-treat bags that we got last year.
Here's the t-shirt version of our costumes that we wore to Disneyland.