I realize that you're looking at an expansion of web siteS...
My recommendation if you're looking for advertisers for the existing neighborhood site that is already proving to be successful is to go to all the neighborhood businesses and sale ad spots to them (restaurants, hardware stores, craft shops, etc...). From there you can get statistics from click-thrus, sales, etc... to use as a media kit for your next community site.
Best of luck in your online endeavor,
Elizabeth
1-2-3's of Internet Marketing - Get the Attention You Deserve