Review the major shopping comparison sites

Shopping.com, shopzilla, nextag, pricegrabber. 

Want to research to determine if it is a better decision to build our
own comparison engine database for our site or if we can partner with
one of these larger engines to be ?powered by? and have a custom
module created for our specific all natural product lines.

Do any of the sites or their parent company offer affiliate or custom
solutions to a corporation for use on its own website with
customization for its specific brands to be compared on the criteria
of its choice?  (Example product ingredients and then add cost rather
than simply cost? )

How do company?s products (HP, Dell) enter the four major?s data bases
to be in the consideration set?

Compare the features and benefits (strengths) of each engine to the
consumer using it and for the company listing products or ?powered
by.?

What area the weaknesses of each shopping comparison from the consumer
point of view and for the company?

What is cost associated with being an affiliate or powered by the engines? 

What is the address and correct contact with correct contact person
for each company?