After taking a look at the referrence website you're provided, the Map Radius Calculator and going through your requirements - most of which request the exact same functionality as with the referrenced website - I'll implement the expected Google Maps (or Bing Maps) with the draw circle, edit cricle and clear options. This shouldn't take long, personal estimate is within one day, however I've listed the worst case scenario of two days.
This would imply clear and concise code formatting and code comments. If necessary I can even futher explain how everything functions together. With that being said, we can always discuss the details before, during and after the project to further ensure a satisfactory partnership.
I've worked on countless websites for various clients, from political parties to portfolio sites for individuals. Which included static programming, designing and personalization of the front-end and back-end, including website maintanence; hence I'm highly familiar with operating on and with websites.
Sincerely,
M. Grgich