The best expression to add to sentence 2 to clarify the relationships among Paco's ideas is D. However.
This choice introduces a contrast between the growing necessity of having a college degree for many jobs and the increasing expense of attending college. The revised sentence would emphasize the contradiction between the need for higher education and the financial barriers that prevent access, which is central to Paco's argument for abolishing tuition.
So the modified sentence would read:
(2) However, going to college-even a public college-is becoming more and more expensive.