From the numerous times it's happened and then been talked about here, my understanding is DDOS is pretty cheap. And even if you want to get the heavy duty attacks, you're not getting near the millions unless you want it both high-strength and permanently on for months at a time.
In total over the last few years I can see the grand total between all vectors getting into the six figures, but to get to millions the majority would have to not be on the level of whatever a troon can buy with their tugboat for the month.