Some of the main things that will need to be done are:
• Add a code generator for craigslist postings so that users can copy and past the code into their [url removed, login to view] postings.
• Listing templates for cars, service, realestate
• Add design themes which are basically saved customization parameters that can automatically be applied to new listings
• Make the listings multi-page like the Postlets Plus listings
• Add Google AdSense ads to the listings
• Add a customizable portfolio page that displays links to all of a specific users listings
Of course this is very general, but this is just to give you a general idea of what I want, so you can give me a very rough estimate of the cost and lead time. Then depending on the estimate we can talk over the specifics.