Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Idaho Falls to Killeen as you normally would.
IDA stands for Idaho Falls Fanning Field Airport, while GRK stands for Killeen Fort Hood Regional Airport. These codes are often called IATA codes, a set of identifiers established by IATA (International Air Transport Association) that is widely used by airlines and the aviation industry.