It's not cheap to ride the T. But, as with most public transportation systems, fares don't produce nearly enough to maintain the system. Throw in debt service and things get worse. From an op-ed by Charles Chieppo:

How debilitating is the MBTA's debt? The agency paid more in debt service last year than it collected in fares. When debt service is included, fares cover just over a quarter of the T's costs.

The money to pay debt interest and maintain the T has to come from somewhere. The State is broke. I expect that the working people who depend on the system will be asked to pay more to keep the T afloat. That does seems to be the pattern. And, as Chieppo notes, with plans to expand the system, service and maintenance will suffer system-wide, impacting discretionary ridership and putting more on the shoulders of those who have no choice but to use public transportation to get to work each day.