We went to Paris for the day last March and i think the Mobilis ticket was E16 per adult. my daughter was free because she was under 4 and we paid for my son who was 8 and it came to around E40 return. I seem to recall that the last return train to Disneyland was around midnight. Its very easy to do and the best stop for the Tower is Trocadero (check spelling). Wonderful views of the tower.