Drupal – One Noder per User per node reference by FlightDriver

I am using entity url reference to create nodes of content “b” with reference to content “a”. What I need to do is limit users to create only 1 content of content “b” per content “a” per user. So User A creates content B reference Content A… (Budget: $30-$35 USD, Jobs: Drupal, Graphic Design, HTML, PHP, Website Design)