Hi goldbry! First of all congrats on the publishing deal! Second, once you find someone you can have your drawing scanned at any kinkos or many office supply stores also have a copy/print service which includes scanning. As far as the rate goes, your artist will negotiate with you on it. I'm happily surprised that your editor is suggesting that you provide a map; there are many aspiring novelists around here making maps and most of the resources I've found have said the publishers usually like to hire people themselves.
Sounds like a great project, I'm sure you'll find someone very soon!