i don't know pricewatch, but most of these sites have contracts with the companies they list, so when they say they are searching the web for the best ideas, they are really searching the companies that pay them to be listed.
to do this, you'd need to know the structure of the website you want to scan - ie where the relevant stuff is in the outputted html.
Then get the file using file(), and using the regular expressions functions to search through it for the relevant markers/strings.
you'd have to put in some routine for flagging when errors are returned, so that if a page design changes, you can update their code. The commercial sites agree terms with their partners so that they can be prepared for code/design changes.
good luck!
