An Apex developer has sold off an apartment complex that was part of a larger, 300-acre site the company purchased at the edge of Research Triangle Park on Ellis Road in Durham. Halle Building Company sold the Reserve at Ellis Crossing complex for $61.25 million. The recently-constructed apartment community was built on 31 acres, near the intersection of Ellis Road and Highway 147. The buyer is a subsidiary of Duck Pond Realty Management, a New York-based investor group that has been active in…