In less than a week, nearly 100,000 people have signed an online petition demanding the sum be reimbursed and then given to charity.
"How can we accept the First Lady exploiting her position to fund something that amounts to a private expense when all of us are being asked to make sacrifices?" it asks.
Another viral protest #CarlaFaitesUnDon (Carla Make a Donation) is spreading on Twitter.
In June, employees at Air France leaked that Bruni was given a free first-class Paris-New York round trip - cost 8395 - to promote her album.
"I thought the monarchy had been abolished," quipped Leon Cremieux of the trade union SUD Aerien.
Mischievously offering a touch of compare-and-contrast, the Government has disclosed that Valerie Trierweiler, the partner of Sarkozy's successor, Francois Hollande, employs five staff at a cost of 19,742 a month. In the twilight of Sarkozy's 2007-2012 term, Bruni spent 60,000 a month for twice as many people.
Bruni's lawyer says she is outraged at insinuations of misuse of public funds and will take legal action "against remarks which damage her honour". Air France points to laws passed in 1955 and 1985 granting free travel to former French Presidents and their spouses on the national carrier and train service.
Bruni, 44, was one of the first generation of supermodels.
When she aroused the interests of the newly elected and freshly separated Sarkozy, few eyebrows were raised about her past. But many questioned whether she would make a decent First Lady.
She largely silenced her critics, carving out a role for herself as someone who added glamour to her dour husband yet was no brow-mopper. She attended occasional banquets and other ceremonial engagements, set up a foundation for the disadvantaged and launched a successful career as a singer-songwriter.
Underpinning Bruni's problems today is the fuzzy demarcation between public and private interests, frequently an issue in France.
In the good times, the Elysee's stellar spending was never scrutinised seriously - indeed, many may have thought lavishness vital for promoting France's chic image.
Today, times are harder. In just 14 months budget cuts, unemployment and Hollande's more austere lifestyle have changed the mood. People are starting to look at how every centime is spent and there is palpable anger at waste. Frivolity and ego are out of fashion. Or to put it another way, France has changed model.
