Housing prices may be down, but the cost of a coveted parking space is up.

An unidentified buyer yesterday paid $300,000 for a private parking space in the Back Bay, making it the most expensive parking space in Boston, according to Listing Information Network, which tracks the city's real estate market.

Debra Sordillo, the Coldwell sales agent who brokered the deal, said several residents at 48 Commonwealth Ave. engaged in a bidding war for the space, driving the asking price of $250,000 up to the record-breaking $300,000. The winning bidder did not want to be identified, she said.

The price is more than what many people pay for a house, but Sordillo said prime parking spaces near the Public Garden are in short supply.

"There's only so many parking spaces in the city," said Sordillo. "And in this part, there's very few."

In the last year, parking spaces in the Back Bay and Beacon Hill have fetched an average selling price of $134,000, Listing Information Network said. A year earlier, the average cost of a parking spot in those areas was $127,000. The number of parking space sales has also increased in the last two years, from 18 in 2007 to 26 last year.

The owners who sold yesterday's record-breaking parking space live in the historic brownstone at 48 Commonwealth, a multi-unit building prominently located on the corner of Commonwealth Avenue and Berkeley Street. Sordillo said they are also attempting to sell their posh two-bedroom unit with direct elevator access. The $2.5 million price includes a parking space in the building's underground garage.

The $300,000 space came with few amenities other than the prime location; it is outdoors and uncovered.

The previous record for an open-air parking space was set in 2006, when a buyer paid $250,000 for a space behind 31-33 Commonwealth Ave.