Is there anything I can do?

I moved 1/2 way across the world for a job as a massage therapist. I was hired and had my e-ticket, when 3 days before I got on a plane, I recieved an email that had the details of our schedule to come and in fine print was "please be advised a drug-test will be part of the process". I went and I took the drug-test and unfortunately failed. I was fired and was told I had to pay the transportation costs back per my contract ( although there was no specifics on length of re-payment ). There were 3 other people who had taken tests and their results came back inconclusive due to too much water in the urine ( these people were never re-tested, yet I was fired on the spot ). If my previous employer is really a drug-free work place, shouldn't they have re-tested those employees? It seems a little disciminatory to me, but I don't know. I am going to be sued for the whole plane ticket amount and I was wondering if there is anything that can be done? I need help. Any hints or a push in the right direction would help.