1a is correct
1b and 1c do not make sense. 1b can be corrected like this:
"He betrayed the cause that he had been paid to support." ("that" is optional)
2a,b,c do not make sense. However, I think I can tell what you are trying to say. I would say it like this:
"He told us about the life long goal for whose attainment he had overcome so much danger and toil." or
"He told us about the life long goal he had endured so much danger and toil to attain."
3a,b,c do not make sense. If you explain what you are trying to say, I can correct it.