Manhattan loft prices set a new record in August as the median price per square foot reached $966, according to a monthly market report from Halstead Property. That’s a 25 percent increase over August of 2004, and keeps with the general trend last month of Manhattan apartment prices increasing. The average apartment price in the borough for August was more than $1.14 million, according to Halstead, 14 percent higher than the price a year ago. The median price also increased by double digits, to $725,000. The Halstead report cited low interest rates and a tight inventory as reasons for the increases.