This 1989 article says that Stephen Spielberg bought the surviving sled for $55,000.
http://www.nybooks.com/articles/1989/06/01/remembering-orson-welles/

"I thought you were class,like a high note you hit once in a lifetime."- Young Man With a Horn(1950)

For the final scene, a stage at the Selznick studio was equipped with a working furnace, and multiple takes were required to show the sled being put into the fire and the word "Rosebud" consumed. Paul Stewart recalled that on the ninth take the Culver City Fire Department arrived in full gear because the furnace had grown so hot the flue caught fire. "Orson was delighted with the commotion", he said.
BUT :
Sled of 'Citizen Kane' Brings $60,500; Sled in 'Citizen Kane' Is Sold for $60,500
New York Times :Published: June 11, 1982
Rosebud, the sled made for Orson Welles's classic 1941 film ''Citizen Kane,'' was bought Wednesday afternoon by Steven Spielberg, the director-producer, for $55,000 at Sotheby Park Bernet.
The addition of the 10 percent buyer's fee made the total price $60,500.
The sled, one of three balsa versions made for the final scene of the movie, is the only one that survived the filming.
The other two were burned in filming a scene in which a workman tosses the sled into a furnace.
Describing ''Citizen Kane'' as ''the most classic movie ever made,'' Mr. Spielberg, who bid by telephone from Los Angeles, said the sled was ''a symbolic emblem of quality in the film business.''