Deborah Sousa was facing a decision familiar to many Boston-area residents: with rents steadily rising and a shortage of suitable alternatives, did it make more sense to continue renting or take the plunge and buy a property?

Sousa’s decision related not to a primary residence, but a new headquarters for the Massachusetts Mortgage Bankers Association (MMBA). After a leasing space in various downtown Boston office buildings over the past four decades, the organization purchased a 1,340-square-foot office condo at 185 Devonshire St. last week for $425,000.

“I felt like a first-time homebuyer,” said Sousa, the association’s executive director. “I kept going back and checking the numbers. It is taking a chance. You’re depending upon the real estate values remaining constant or increasing eventually, but you don’t have a magic ball.”

Sousa spent recent months making cost comparisons between renting and owning over the long term. Office rents have steadily risen downtown as occupancy rates have recovered from the recession. Average asking rents for class B office space in the central business district were $36.45 per square foot at the end of 2014, according to Cushman & Wakefield research.

The MMBA’s expiring lease at 21 School St. was significantly below market value, said Michael Sinclair, the association’s 2015 chairman.

“It was clear when the term was up we were going to have to pay market rates. That’s what prompted our search,” said Sinclair, a vice president at Hingham Institution for Savings.

Moving to the suburbs wasn’t an option, because Sousa spends much of her time on Beacon Hill lobbying on the group’s behalf.

Arlington-based Leader Bank gave the group a 25-year mortgage with a sub-4-percent interest rate. Monthly payments, including condo fees, will be less expensive than renting, Sinclair said.

“The board wanted to focus on buying something that would rise or hold in value, as opposed to going into the suburbs where the prices might be a little bit more volatile,” he said.