Developer for my site

I am looking for a developer that can integrate ecommerce functionality with a web site. Please state which ecommerce solution and payment gateway you feel would work best for these requirements, and your price and timeframe to build it out. The ecommerce piece should appear seamless with the rest of the site, and have the same look and feel. The shopping cart must remain on our website and not take you to an external website. General Requirements: -WYSIWYG: must be able to make updates to products, pictures, pricing, etc. through a WYSIWYG editor and easy for the non-HTML savvy person to edit. -SEO: must be search engine optimized and friendly -Single signon : ecommerce solution should utilize the so the visitor only has to enter login information once and the checkout process uses the same information -Cookies: should allow easy access to remember stored user data to pre-fill existing buyer information fields.