Dealer Locator with Google Maps Showing Location

One of our clients wants to have a dealer search function on their website that works something like [login to view URL] (see dealer search function on bottom right of page.. enter L4C 0A8 to test). This would be for Candian Postal Code lookups only (dealers are based in Canada only). So user enters their postal code and sees the closest 3 dealers with their locations pinpointed on Google map. I'm open to using any existing software that does this (open source or fee based). I'm also open to alternate lookup methods (text listsing with closest proximity displayed). Looking for the most cost effective solution. Client works with 50 dealers. If additional software is required, please include all inclusive costs in your bid.