Artist Commission Questions

first time on stackexchange. I am currently seeking wisdom in terms of commissioning an artist. Straight to the point: I would like to commission a majorly famous anime artist for 1-2 pages of full colored digital fanart. In this case, Masamune Shirow (you see what I mean by major).

Question: How would I best go about setting something like this up in terms of contacting and arranging the request? To your best educated guess, how much money would I be looking at for this endeavor? This is just for my own comparison purposes.

Note: -I have commissioned a number of visual novel/doujinshi artists in the past. Highest amount I've paid thus far was around $560-$600 for a full colored digital work of 3 characters.

-I've looked around the net for fine art commissions and rare original comic book covers to get a ballpark estimate, but I'm looking at between $5000 - $30,000 USD. Sound about right?

This is a pretty serious endeavor so please mention anything, absolutely anything else I might have missed/overlooked.