Hi!
I've been in the development business for 4 years now and I believe I can help you in this project.
Recently I had to deal with a project that is quite like yours, and that gives me a good perspective of what to do and how to do it.
Sadly, it's not an easy job, to integrate the project with Google Maps API. You see, the site you showed us in the job description has a map that is just an image, so it's not integrated with Google Maps. It would make things a lot easier, but when it comes to using geolocation as position for the markers, it can be complicated and take some time.
But I assure you, it's a fair price, for a good and trustable work.
Let me explain the milestones:
First, the HTML and CSS
These are the two bases of the project, that will define the structure of the site and it's appearance.
This will take about 1 or 2 days.
Second, add tags and markers functionality
Here, I'll be programming the funcionalities that you specified in the description: the option of adding (and I assume deleting too) new tags and new markers in the map.
This will take about 1 or 2 days also
And finaly, complete the integration with Google Maps
By the time I proggramed the new markers appearing, I'll have to position it accordingly as I move the marker arond the map.
This will take about 3 or 4 days.
The extra days will be for fixing any bugs that appears.
Please contact me if more info is needed.
Thanks for your attention and I really hope to get this job.