Hi Jay
The big problem with answering this question, is: how do you define an "average" person?
From memory, Sun suggested that
if you are already familiar with all the technologies you will be using in the project(as in: you have already used them all)and you are familiar with the alternatives (so you can describe in your documentation why you chose to use your implementation and if you put in an average 40 hour week, then
you should be able to complete it within about 3 weeks.
Of course if you need to learn some technologies (and most people do learn new things working on this project, even if they don't necessarily
have to use the new things), or if you have to investigate other options, or if you cannot dedicate the next 3 weeks to working on this project, then it may take you longer.
The oposite is also true: if you can dedicate more time to this project, and you are already expert in what you will be using, then you can complete it in far less time.
Regards, Andrew