How much Diana Ross earns for a concert?

[Nitro2015]

I was wondering what would be more or less the value that Diana Ross earns when performing each show of a tour?

In fact, I always think about this issue for any artist, because I do not know how the promoters can generate profit from a tour since the expenses to perform the show are usually exorbitant [[especially in the case of giant tours like U2 and Madonna, for example).

And, in Diana's case, I wonder why she has not toured Europe for so long. She is so huge there and could easily sell out arenas or, at least, large theaters.

I know she's not keen to travel overseas that often, but she doesn't go there to perform almost ten years.