Claes Oldenburg’s 1962 sculpture Floor Burger — a four-by-seven-foot painted canvas stuffed with foam rubber and cardboard boxes — caused an uproar in 1967 when the Art Gallery of Ontario (AGO) purchased it from New York’s Sidney Janis Gallery for $2,000. The acquisition of the giant hamburger sparked a protest from a group of art students and teachers from Toronto’s Central Technical School. They created a nine-foot-tall bottle of ketchup in response, paraded the bottle in front of the museum, and tried to donate it to the institution.

The AGO, which had already emphasized that no tax dollars had been spent on the burger, politely declined, later explaining in the Toronto Telegram that the faux sandwich was significant as it “represents Oldenburg’s introduction of soft sculpture.” Oldenburg, for his part, said the incident didn’t hurt his feelings at all, noting that his work would “get old soon enough.” He did, however, wryly suggest that the students who created the ketchup bottle “ought to have made it out of something softer.”

This spring Floor Burger will return to New York, to the Museum of Modern Art, as part of “Claes Oldenburg: The Street and The Store,” which opens April 14.

Oldenburg’s soft sculptures remain among his most sought-after works, but experts say it is difficult to pin down a price because these, like the later, large-scale works by the artist and his late wife and collaborator Coosje van Bruggen, rarely arrive on the market. (Van Bruggen passed away in 2009, though Oldenburg, 84, is still producing new work.)

“No one’s going to release major soft sculptures for less than $10 million,” says Marc Glimcher, president and director of Pace Gallery, which has represented Oldenburg since 1990. But, he adds, “it’s hard to know” exactly what they would fetch because it’s been at least two or three years since a top-caliber work has sold. “Would I recommend that the most famous Oldenburg object be insured for $10 to 15 million, $20 million? Definitely.”

Such lofty eight-figure values are not reflected in the auction market, where no major collaborative sculptures have sold and where just three of Oldenburg’s works have broken the $1 million mark. Auction prices have topped out at $2.2 million, the price achieved for Typewriter Eraser, 1976, at Christie’s New York in May 2009. The second-highest auction price was achieved for a much smaller, enamel-on-plaster sculpture from Oldenburg’s early, “Store” period, Yellow Girl’s Dress, 1961, sold at Sotheby’s New York in May 2008 for $1.7 million.

“There isn’t a lot of work by Oldenburg that’s easy to get one’s hands on,” Glimcher says. That’s because so many of the most important works are held by institutions and also because “people do not like to sell their Oldenburgs.” Glimcher says he lives with 10 of the artist’s works and couldn’t part with any of them, especially his hanging maquette of Giant Soft Fan, 1967, which he counts among his most prized possessions.

Oldenburg works on paper are more widely available. “The drawings are fantastic, and they can sell from $15,000 to $300,000,” says Anthony Grant, executive vice president and international senior specialist in contemporary art at Sotheby’s. “Claes is a great draftsman. There’s no question about it; there’s no greater hand.”

The Blouin Art Sales Index lists hundreds of works on paper and multiples that have sold at auction for five- and six-figure prices. A number have fetched more modest, three-figure prices.

“The minor, lesser-known works, or the editions, the multiples, come up more frequently,” says Jennifer Yum, vice president and specialist head of day sale, postwar and contemporary art at Christie’s. “A beautiful drawing from the ’70s or ’80s would be a perfect acquisition for someone who’s trying to enter the postwar market,” Yum says. “They’re reasonably priced and they still have a beautiful sense of his hand and whimsy.”

Steve Henry, a director at Paula Cooper Gallery, which frequently handles Oldenburg and van Bruggen’s work, says prices for recent small notebook drawings range from $45,000 to $50,000, quality works on paper from the early ’70s typically sell for prices from $75,000 to $150,000, and “works from the ’60s will be slightly more.”

Sculptures are much rarer but also available: A pedestal-mounted 2009 painted cast aluminum sculpture by Oldenburg and van Bruggen, of cherry pie, titled Paradise Pies (II), 2009, from an edition of six, is currently available for $150,000, Henry says, adding that a major work from the ’60s would be “somewhere in the $3-million-to-$4-million range.”

The upcoming MoMA exhibition narrows the focus of the touring show it is derived from, titled “Claes Oldenburg: The Sixties,” and organized by the Museum Moderner Kunst Stiftung Ludwig Wien (and already presented in Vienna, Cologne, and Bilbao). The MoMA show zeroes in on the early part of the decade, when Oldenburg lived in New York, and covers his output only through 1964. It focuses on two of his most important bodies of work.

“The Street” is a rarely exhibited installation of objects, inspired by daily life on the Lower East Side in the late ’50s, with crumpled and torn everyday materials like cardboard, newspaper, and burlap, and intended to suggest a busy street scene populated by cars, barking dogs, graffiti, and figures. For “The Store” Oldenburg rented a small storefront on East 2nd Street in 1961 and filled it with rough painted-plaster renditions of commonplace goods: shoes, cigarettes, a piece of cake, a girl’s dress. Visitors could take home an object, such as Big Sandwich, 1961, for $149.98. Oldenburg repeated the project in various iterations; some of those objects will be incorporated into the exhibition.

In the second-floor atrium, MoMA will show Mouse Museum and Ray Gun Wing, two architectural structures created in the 1970s that present ready-made objects next to a range of experiments from Oldenburg’s studio.

The son of a Swedish diplomat, Oldenburg was born in Stockholm, grew up in Chicago, and returned to Illinois after earning a degree in literature and art history at Yale University in 1950. But it was in New York where he came to prominence after moving there in 1956 and finding a community of artists ready to challenge the status quo.

Ann Temkin, who curated the MoMA show, says, “after the decade of Abstract Expressionist dominance of the art world, all of them” — Oldenburg, Roy Lichtenstein, Robert Rauschenberg — “were saying, ‘How can we make something that isn’t so precious, so high-minded, so reverential?’” Temkin says. “It was clear that there was going to be something new and that it would have a lot to do with the grittiness of New York City and with ordinary consumer goods.”