The sea of empty seats was especially stunning because the Minutemen had been accustomed to nearly packing their campus stadium for homecoming games. Over the previous five years, they had played before average crowds of 13,937 at the 17,000-seat McGuirk Alumni Stadium, on the UMass Amherst campus.

The program’s precipitous attendance drop at Gillette — never more evident than when the Minutemen completed their 1-11 debut in the elite Football Bowl Subdivision by losing to Central Michigan before a paltry 6,385 — has driven up the cost of the school’s effort to enter the ranks of big-time college football and intensified concerns about the upgrade’s prospects for success.

With students and taxpayers picking up the tab for at least some of the cost overruns, the lower-than-expected attendance has prompted some to wonder whether UMass should reconsider its plan to transform the Minutemen into a national football program.

“I think we certainly need to get out of the FBS experiment,’’ said Max Page, an architecture professor who co-chairs a campus committee examining the cost. “There is a feeling of urgency because of the disastrous attendance this year, which contributed to higher costs than we expected. They already were bad enough.’’

By nearly every indication, it appears UMass alumni, whose support for the upgrade was considered vital, have yet to embrace the initiative.

“We have long been told that one important reason alumni support for UMass is so mixed is that we didn’t play FBS football,’’ said Ernest May, head of the university’s Faculty Senate. “Well, we have now played FBS football in a great venue located right in the backyard of where most of where our alumni live, and the silence was deafening.’’

Subpar ticket sales have contributed to a $715,000 cost overrun, increasing the budget for the football program’s inaugural season in the Mid-American Athletic Conference to more than $7.1 million — up from $5.4 million in 2011.

By that measure, the university spent an additional $1.7 million this season, only for the average attendance to decrease to 10,902 from 13,008 the previous year. (In 2011, the Minutemen drew 41,018 to four home games on campus and 24,022 to a “home’’ game against New Hampshire at Gillette.)

Students and taxpayers will fund about $5 million of the $7.1 million budget through institutional support, including student fees and direct public subsidies.

“One thing we have learned is that it’s going to take us a while longer than we had perhaps anticipated to build a regular fan base,’’ UMass athletic director John McCutcheon said. “It’s not going to happen overnight.’’

With the vast majority of UMass-Amherst’s 400,000 Massachusetts alumni living in the eastern part of the state, school officials had projected average crowds at Gillette of about 20,000. Instead, attendance dropped by 7 percent from the 11,737 the Minutemen had averaged on campus the previous five years.

UMass-Amherst chancellor Kumble Subbaswamy, who inherited the football plan when he took office last summer, said he was generally satisfied with the inaugural season and will evaluate the initiative annually. He attributed the lackluster ticket sales in part to the leadership transition from the previous chancellor, Robert Holub, who spearheaded the upgrade.

“If this keeps up, then it will become a concern,’’ Subbaswamy said. “But we are still in the very early stages of the transition.’’

Bill DeFlavio, a UMass Hall of Famer who was an All-America lineman for the Minutemen in 1971 and heads the Friends of UMass Football, said the school’s alumni are not naturally interested in games against new conference opponents such as Bowling Green, Central Michigan, and Buffalo.

The Minutemen previously had played regional rivals such as New Hampshire, Maine, and Rhode Island.

“There are plenty of alumni out there, and the university put a tremendous amount of effort into promoting the games at Gillette,’’ DeFlavio said. “But it just hasn’t resonated enough to put people in the seats. I don’t know what the answer is.’’