The correct answer is 2 "My parents say that if I’m going to go, I have to pay for either half of the trip myself or pay for all of my spending money"
Explanation:
In grammar, a parallel structure refers to a sentence in which there is a repetition of a grammatical form of structure in the case of conjunctions such as the words and, but, nor, etc. parallelism occurs in a phrase when conjunctions tie two elements of the same type and besides this, conjunctions are used correctly, especially in the case of correlative conjunctions such as not only/ but also; either/or, neither/nor, etc as each of these pairs should always go together.
Considering this, the sentence with a correct parallel structure is "My parents say that if I’m going to go, I have to pay for either half of the trip myself or pay for all of my spending money" because in this sentence the conjunction "either" is linked to the conjunction "or" which are correlative conjunctions that always go together and also in this case the conjunctions link to elements of the same type "pay for half of the trip" and "pay for all of my spending money" which completes the parallelism.