Directory Project for Wordpress Site

We are completing the design of our website and it is done using Wordpress. We will be launching it soon but we want to create a directory as part of the site that will allow therapists to list their businesses. We want it to allow therapists a choice to sign up free with limited features or also give them the choice to pay for an upgraded listing with more features. We also want them to be able to upgrade later from the free option to an upgraded listing. Where the actual directory is displayed, I want there to be a search function by zip code. We are using Wordpress. We are currently using WishList member for the membership portion of our site so this directory membership of therapists cannot conflict with that at all please. It needs to be a separate. I need someone who is an expert with Wordpress and programming so please don't respond if you do not qualify. I would like to see samples of your work done with Wordpress programming so please make sure to show some samples. Also, please quote a total fixed cost. This shouldn't be a huge project especially if we simply customize the plugin listed above. I am looking for a programmer for other long term projects so this will be a stepping stone.