Drupal module creation to live sync user accounts between Drupal 7 and external custom MySQL DB by stemp

I need a module to both way synchronise user accounts, between Drupal 7 and external custom MySQL DB. When insert/update data in user accounts table at an external (non Drupal) MySQL database, then this data should be used by the module to make the same changes at the Drupal 7 user accounts table... (Budget: $30-$250 USD, Jobs: Drupal, MySQL, PHP)