With the end of Mercury, attention turned to Gemini and Apollo. Both programs were growing like mad - in the case of Gemini, growing out of control. Originally budgeted at aronud $530 million, it was now expected to price out at twice that - or more. Every element of Gemini cost more than the original estimate: the basic spacecraft, the Titan 2 launch vehicle, the Atlas-Agena target vehicle, the ejection seats, the fuel cells. Money was spent on the idea of flying Gemini to touchdown on return to earth using an inflatable wing a plan that never really had a prayer of working, but it ate up a couple of years and a few million bucks. (The North American test pilot for the Rogallo wing happened to be Jack Swigert, my former roommate from the astronaut interview week.)
SOURCE: We Have Capture: Tom Stafford and the Space Race by Thomas P. Stafford with Michael Cassutt