The best revision that creates one complete, controlled sentence is:
B. Sometimes students make budgets in order to buy or do something special in the future—such as buy sports equipment or go on a class trip—to accommodate this future expense, students will need to create a budget to find out how much money they’ll have to save each week in order to meet their goal.
This option uses em dashes effectively to set off the example, while clearly linking the two parts of the sentence. It also maintains appropriate punctuation and word choice for clarity.