I have a customer who want to build quite a special website.
Basically, he wants something like CNet (but in a much smalle scale), a product information and reviews site, but dedicated to mobilephones only (maybe later on includes other digital products as well).
Besides some normal functions that can be found in any CSM (such as news, pools, gallegy, links, download database, discussion board...), the main part of the website is a mobile phone database, that has the following main features:
- Images, editor reviews & rating, customer reviews and rating... associated with each phones
- A phone manufacturers list
- Phone specs (as detailed as possible, he wants to has separate field for each spec like dimensions, band, each feature... so that customers can compare phones)
- Phone prices from different stores: A system where store owners can login and enter their price for each phone, these prices will be display when phone is viewed.

I have serveral options, but haven't decided which one to choose:
- Start from scratch: Not too hard to do, but with all the basic CMS functions above, it's just waste of time writing all those stuffs.
- Write a modules for an existing CMS: Seem to be the best option, but which CMS to choose? I prefer PostNuke or Mambo, but I am not sure if that the best one for this job.
- I don't expect something like this already exist, but do you know any similar system that I can modify for this site?

Any comments is welcome
Thank you