I'm an "unknown quantity" but I would like to do this for you. It's an opportunity for me to start building a portfolio since I've lost all my old maps I did a few years ago.
I use inkscape as my primary tool. I started playing around with your sample just to see if I could do it, and I think I could make something pretty cool, and similar to your examples of the styles you like.
Send me a pm when you see this, and I'll show you what I've got so far? I can understand not wanting to go with an unknown, but maybe we can help each other out?