I am in the SAME exact situation. I got into Emerson and MGH, but also got into state school which would cost me the same around $15,000 for two years. I thought about it a lot and for me it just did not seem worth it. I didn't think I could justify spending $80,000 more than I needed to for my education when many people have told me that to many employers where you got your masters does not weigh heavily. I looked at the salaries for SLPS on ASHA's website and from what I found one of the biggest indicators of salary for all areas of the field was how many years of experience you had under your belt, not where you went to school. The state school, similar to MGH and Emerson, had 100% job placement (as many schools probably do since SLP is high in demand) as well.
Whatever you decide, I think if you work hard you will be able to pay off your debt but it will take time. For me it was extremely difficult to say no to MGH because I have wanted to go there for years and I am such a competitive person. However, I just needed to take a step back and realize that in the end I don't need my career to be the center of my life. I want to eventually settle down and have a family and be able to enjoy life, which will take longer to do if I am on a 30 year plan to pay back my loans.
It is all about finding the perfect fit for you, so if you feel BU will offer you opportunities that are important to you that it is worth paying the extra money, I say go for it. I know it is such a difficult decision!! Good luck