For $900 and no possibility of a less expensive, previous day(s) flight I might risk it. I would be concerned about your Raleigh to FRA flight being delayed but you can have a plan B and C ready to implement.
I would be aware that jet lag could affect your first day or two but our experience has been this. When the 2 of us fly to Europe we almost always have some mild jet lag flying over. When we’ve met up with friends or family members on day one we just roll with it, jump right in and rarely have jet lag. Maybe you’ll be one of those types who will be energized by your enthusiastic group who will be gathered in Köln. It a hard call and I could see myself weighing the risks too. Good luck with your decision.