Amazon.com Inc. said it's launched its one-hour delivery service in New York City's Manhattan borough. The new Prime Now service will cost its Prime delivery customers in Manhattan an extra $7.99. Two-hour delivery will be free, Amazon said. Amazon will use its new building on 34th Street in Manhattan as its delivery hub. One-hour delivery service will be expanded into "additional cities" in 2015, Amazon said. "Prime members in Manhattan are going to love this service and we cannot wait to roll…