Barbara Spencer, who lives near Brooklyn Heights, is thankful that she bought her propane when she did. “I bought it low when it was $2 a gallon,” she said. “I got 200 gallons. That cost me $400. It went to $3, and now it’s $3.50. “If I had waited, 200 gallons would have cost me $700. I don’t know how we are going to do it if prices stay this high.”