If Bryn Mawr ends up being cheapest, go to Bryn Mawr. The quality of education is excellent, and its reputation exceeds UMD and Pitt by a margin as an undergraduate distinction. Those latter two are schools I would consider for graduate study in your intended discipline, and for undergraduate if they were less expensive, not more. Your parents may not understand that those impressive things about the larger universities are not able to benefit you as directly as the strong, dedicated resources at a top LAC like Bryn Mawr.