You are going to have to scrape the websites in order to get model and price information. You can buy scraping software
http://www.mozenda.com/Scrape-Website.aspx
or you could write your own using PHP cURL.
http://php.net/manual/en/book.curl.php
You are going to have to define scraping templates for each site in order to target their stock lists
many companies do not endorse this practice and if they change their site then your site will break or at least the feed will