the 1948 Bowden Spacelander bicycle, made of fiberglass when it was a big fad, but less than a thousand were made, they were too expensive

The Spacelander is a marvel of postwar biomorphic design. Its curving lines and amoeba-like voids represent the mutation of the prewar streamlined style into a new expression based on organic, rather than machine-made, forms. “Britain Can Make It” exhibition in 1946. Conceived in aluminum, the dynamic form featured a direct drive hub dynamo that stored the downhill energy and released it on uphill runs. The originally prototype for the exhibit was hand-made by the MG Auto Company. Due to the expense of manufacture, the bike did not go into production until 1960, when Bomard Industries of Grand Haven, Michigan contracted with Bowden to create the finished product. The final design was produced in fiberglass and built-in headlight and taillights were added. Ultimately, Bomard Industries went of business and only 522 examples were ever produced.”

http://www.howtobearetronaut.com/2010/08/spacelander-electric-bicycle-1946/ and
http://www.brooklynmuseum.org/opencollection/objects/2587/Spacelander_Bicycle

According to a Yahoo Answer contributor:

Strangely, the Spacelander was designed about 1946 in aluminum but not placed into production until 1960, so if he has the original 1951 fiberglas prototype it's value is inestimable. A mint 1960 version has seen pricing in the $10,000 to $12,000 range.

The Spacelander, as you probably already know, was reproduced in the 1990s, and I think they are still available today, these can be had for less than a couple of thousand dollars.

above 3 images are from http://www.nostalgic.net/bicycle206.htm

this may be the one I just saw on TV last night on "It's Worth What?", as Case just took this photo in Burbank, and the sign shows that the bike is from the Vintage Cyclery of Pasadena. (Thanks Case!)

Update May 2022:

I just learned the history of them!

Benjamin Bowden was already something of an engineering savant by the time he'd submitted a design for 1946's Britain Can Make It exposition. 

He'd spent his days post-World War I as the lead body designer of the Humber car factory in Coventry.

 During World War II, his claim to fame was designing the armored car for the use of both Prime Minister Winston Churchill and King George VI, before working with the Healey company on the Elliot coupe just after the war, the first British production car to crack 100 miles per hour

the Bicycle Heaven Museum in Pittsburgh, Pennsylvania, currently houses a small fleet of genuine Spacelanders in his collection. Of those, one particularly rare model painted in Charcoal Black sits on top of a display case in the museum, the tag hanging from the left side handlebar emphatically stating its current sale price, a scarcely believable $38,000.

https://www.autoevolution.com/news/this-ultra-rare-fiberglass-bicycle-is-worth-nearly-40000-heres-its-story-188287.html