Prices will vary on the level of detail/articulation, size of paper, and estimated time to complete. A simple formula I follow for pricing is $24(or €20) per hour, plus material cost, plus shipping/handling, if any.
Shown here are my current watercolor paper size options in Small, Medium, and Large sizes in both US and metric measurements. For large city plans, I recommend utilizing at least a Medium or Large size paper. Smaller areas, or neighborhoods, usually work well for Small sizes. If you have a custom paper size in mind, please feel free to ask me about possibilities.
Any of my maps shown can be made to print on high quality watercolor paper.
If interested in a print or custom map, please contact me via email at firstname.lastname@example.org with your city/neighborhood of interested, requested size of paper, and potential deadline, if any. Then, I will plan to discuss a color scheme with you and give you a quote. Screenshots from Google Earth are very helpful. Generally, I request at least a 3-month time frame to complete an original painting, and a 1 month time frame for prints. I am looking forward to hearing about your interests.