I had an interesting conversation with a cartographer from the guild who goes by the handle Turambar91 on Deviantart. He advised a reduction into a 10,000 x 4414px at 300 dpi map for $600.

While such a reduction in the scope of the project; isn't something that currently interests me, I still wanted to acknowledge that his insight into a baseline sum has been helpful.

His work is stunning; a particularly striking piece was his Dhar Maqda; I love the design of the canyon.

Thank you for reaching out, Mr. Macdonald.