Is sounds like Concierge Care. In theory by charging a membership fee the the doc does not need as many patients to run his business and can spend more time with each patient and provide extra services. $500 a year, though, seems like a low annual membership fee. Look it up "concierge care" in wikipedia
Concierge medicine - Wikipedia for more info. We have some friends back up north who use it and feel it gives them better access to medical services.