Have you tried to use the DTO? I did. They make you fill in a form saying you'll migrate all services (despite the blog post saying that isn't necessary), and then they take up to 12 weeks to make a decision. In my case they rejected it on a formality after 2 weeks and said to try again (the timer starts again).

So in my case that would have been 14 weeks plus the time to migrate away. The egress costs are equivalent to around 17 weeks storage cost. So you save around 1c/gb if they don't find some reason to reject it.