Order Posts by Closest Numeric Values

Question

I'm using custom post types to display properties and have a custom price field assigned to each post. On the property page I want to display a list of four similarly priced properties, two less than or equal to the price of the current property and two greater than the current price. Ordering properties numerically by price is easy enough with wp_query, but how do I only display the closest values to the price of the current property?