You could make it like this:
0 onActivate --> Client -->ifVar [quest done] == 1 [1 2]
1 onVariableTrue --> Client --> Centerprint ["you have already done this mission]
2 onVariableFalse --> Client ifVar [quest completed] == 1 [3 7]
3 on VariableTrue --> Client --> Centerprint ["good work, you have completed the quest!"]
4 onVariableTrue --> Client -->modVar [money] --> add [200]
5 onVariableTrue --> Client -->modVar [quest done] --> set [1]
6 onVariableFalse --> Client --> centerprint ["discription for quest here"]
7 onVariableFalse --> Client -->modVar [quest completed] --> set
i think something like this would work, not tested though :D
Hope I could help.