This is what we need to build:
It should be a site very similar to http://www.showcase.com/ where someone can come search properties based on location, type, price etc. You have this within the plugin already. The enhancement is the user types. There would have to be three types of users.
User 1: Site admin - Admin to be able to control/edit all listings
User 2: Listings Agent - to be able to login and list properties and populate the content for each.
User 3: Renter - The ability to browse available properties
There would be a purchase component per User 2 and 3. User 2 will need to pay to be able to list properties. User 3 will need to pay to get the detailed info on any listings they want to see more on.
This can be as basic as we can make it. If User 2 can simply login and edit forms and view/edit/delete the listings they've added... good enough.
User 3 would simply see a limited listing, unless they were a paid user in which they'd see detailed listings (i.e. adress, more pictures, listing agent info etc).
Feel free to email me directly, or let me know of a way to contact you. I'm looking for a quote :)