Question: What kept the initial costs for The National Air and Space Museum low?
About the article "National Air and Space Museum", section "History".

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The museum was originally called the National Air Museum when formed on August 12, 1946 by an act of Congress and signed into law by President Harry S. Truman.
Some pieces in the National Air and Space Museum collection date back to the 1876 Centennial Exposition in Philadelphia after which the Chinese Imperial Commission donated a group of kites to the Smithsonian after Smithsonian Secretary Spencer Fullerton Baird convinced exhibiters that shipping them home would be too costly.
The Stringfellow steam engine intended for aircraft was added to the collection in 1889, the first piece actively acquired by the Smithsonian now in the current NASM collection.
After the establishment of the museum, there was no one building that could hold all the items to be displayed, many obtained from the United States Army and United States Navy collections of domestic and captured aircraft from World War I.
Some pieces were on display in the Arts and Industries Building, some were stored in the Aircraft Building (also known as the "Tin Shed"), a large temporary metal shed in the Smithsonian Castle's south yard.
Larger missiles and rockets were displayed outdoors in what was known as Rocket Row.
The shed housed at large Martin bomber, a LePere fighter-bomber, and an Aeromarine 39B floatplane.
Still, much of the collection remained in storage due to a lack of display space.
The combination of the large numbers of aircraft donated to the Smithsonian after World War II and the need for hangar and factory space for the Korean War drove the Smithsonian to look for its own facility to store and restore aircraft.
The current Garber Facility was ceded to the Smithsonian by the Maryland-National Capital Park and Planning Commission in 1952 after the curator Paul E. Garber spotted the wooded area from the air.
Bulldozers from Fort Belvoir and prefabricated buildings from the United States Navy kept the initial costs low.
The space race in the 1950s and 1960s led to the renaming of the museum to the National Air and Space Museum, and finally congressional passage of appropriations for the construction of the new exhibition hall, which opened July 1, 1976 at the height of the United States Bicentennial festivities under the leadership of Director Michael Collins, who had flown to the Moon on Apollo 11.
The Steven F. Udvar-Hazy Center opened in 2003, funded by a private donation.
The museum received COSTAR, the corrective optics instrument installed in the Hubble Space Telescope during its first servicing mission (STS-61), when it was removed and returned to Earth after Space Shuttle mission STS-125.
The museum also holds the backup mirror for the Hubble which, unlike the one that was launched, was ground to the correct shape.
There were once plans for it to be installed to the Hubble itself, but plans to return the satellite to Earth were scrapped after the Space Shuttle "Columbia" disaster in 2003; the mission was re-considered as too risky.
The Smithsonian has also been promised the International Cometary Explorer, which is currently in a solar orbit that occasionally brings it back to Earth, should NASA attempt to recover it.
 "See: National Museum of the United States Air Force and National Museum of the USAF #Other Air Force museums"  
The National Air and Space Museum Trophy was established in 1985.
The trophy presented to the winners is a miniature version of "The Web of Space," a sculpture by artist John Safer.
The National Air and Space Museum presents this trophy annually to recognize both past and present achievements involving the management or execution of a scientific or technological project, a distinguished career of service in air and space technology, or a significant contribution in chronicling the history of air and space technology.
The trophy was created for the National Air and Space Museum by John Safer of Washington, D.C., a well-known sculptor and banker.
John Safer retired as chief executive officer of D.C. National Bank. 
Preserved Wright R-1820 engines are on display at the following museums: Fleet Air Arm Museum National Air and Space Museum National Museum of the U.S. Air Force  
The spacecraft is on permanent display at the National Air and Space Museum, Washington, D.C..