Bonhams auctioned the Fonz's Triumph in 2011, and it sold for $87,500, company spokesperson Nick Smith told Autoblog. This sale copies the earlier listing's description and photos but the seller does add the disclaimer that it's "sold in it's [sic] as filmed condition with all its studio scars." That being said, the lack of new details or images raises a red flag for us, especially at the high price.
According to Bonhams' original listing, this 1949 Triumph is the last remaining example of the three from the show. Famous stuntman and bike builder Bud Ekins created the cycle and took it back after Happy Days went off the air. The Triumph eventually ended up at a motorcycle shop in Oakland, CA, around 1990, and a Cycle World journalist discovered it there for an article in 2000.
Fonzie actor Henry Winkler admitted in an interview to only riding the bike once and crashing it. Afterward, the production put the Triumph on a board and pulled Winkler around.
The Fonz's Triumph could be an important collector's item for TV fans, but caveat emptor. If authenticity matters to you, you definitely want to be sure this is the real thing.