The items up for bidding at Palm Beach Modern Auctions included Onassis' handwritten notes to interior designer Richard Keith Langham and Bill Hamilton, then the design director at Carolina Herrera.
Onassis corresponded with both men about clothes and furnishings she was buying from the mid-1980s through her death in 1994.
Letters written by Onassis rarely appear at auction, and the auction house fielded "tremendous interest" in the roughly 20 lots available, said co-owner Wade Terwiller.
Potential bidders related to Onassis' thoughts on her personal style, which included detailed instructions on how she wanted her jackets and pants to fit and pleas for more color in her wardrobe, Terwiller said.
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In one note Onassis wrote to Hamilton, along with her own sketch of a pant suit, she said: "I just love this suit & will wear it everywhere as I am SO sick of everyone constantly in black -- like Mediterranean villages where everyone is in mourning for 20 years."
The auction house says 1,100 people offered bids by phone, online and in person. Co-owner Rico Baca had expected bidding to start from USD 800 to USD 1,200 for each lot.
Fetching the highest bid was a book about Onassis's restoration of the White House, which she signed for Langham.
It sold for USD 4,575. "What fun it would have been to work with you then," Onassis wrote to Langham in an accompanying note on her signature blue stationery.