Jill Biden's 3,600-mile round trip from France to Delaware to spend two days at Hunter's trial could cost up to $345,000... and taxpayers could be on the hook for a huge bill

• It costs $13,816 per hour to operate the first lady's government plane 
• READ MORE: Follow DailyMail.com's live blog of Hunter trial

Taxpayers will pick up the majority of cost for Jill Biden's whirlwind flights between Wilmington, Delaware, and France so she could be  at son Hunter's side during his federal gun trial although the Democratic Party will chip in some funds.

The first lady racked up $345,400 in flight costs, the National Taxpayers Union Foundation estimated, as she boomeranged between the United States and France last week, traveling separately from husband Joe Biden so she could support her family at home while also representing the United States abroad.

Her political party will repay the government for what it would cost for her to fly commercially with taxpayers footing the rest of the bill.

'In accordance with relevant regulations utilized across administrations, the government is reimbursed the value of a first-class fare for these flights to Wilmington and back to Paris,' Jill Biden's office told DailyMail.com in a statement.

The Democratic National Committee, which is funded by donors, will be the entity providing the reimbursement, a White House official told DailyMail.com. 

The East Wing did not provide the dollar amount that was being reimbursed. It also didn't say who paid for the aides who travel with the first lady. 

But a first-class one-way trip from Philadelphia to Paris is $6,655, per a search on google flights.

Jill Biden spent 24 hours on an airplane in the span of three days so she could switch between being at the side of her son and her husband, clocking in four days at the Delaware courthouse and three days in France. She was back at the J. Caleb Boggs Federal Building in Wilmington on Monday.

The White House Military Office determines the final ticket charge and handles the billing. It typically charges the cost of a first-class fee for those who aren't traveling on government business, such as members of the media.

First Ladies generally travel on the plane a Boeing C-32. The Air Force lists the reimbursable rate for use of this aircraft at $13,816 per hour, the National Taxpayers Union Foundation told DailyMail.com.

The group analyzes official government travel as part of its work, including the hourly rate to operate Air Force One.

Per TravelMath.com, a flight from Paris, France to Wilmington, Del., takes 8 hours. That would put the cost of each leg of the trip at $110,528. Adding in the three flights between France and Wilmington, plus Jill Biden's one-hour flight from Washington D.C. to Wilmington on Tuesday, that is a total of $345,400.

As first lady, Jill Biden does not have the option to fly commercial due to security requirements. Where ever she travels, she is accompanied by her Secret Service detail and several aides along with logistical support staff. 

She has logged a full day of air time to be at her son's side while he fought federal gun charges and then to join her husband as he honored D-Day veterans on the 80th anniversary of Normandy. 

The first lady flew to Wilmington on Tuesday evening. The president dropped her at her plane on the tarmac at Joint Base Andrews and then boarded Air Force One to travel to Paris. 

Jill Biden spent Wednesday in the courtroom and then traveled to France that night. 

She spent Thursday at D-Day festivities in Normandy and, that evening, returned to Wilmington so she could spend Friday in the courtroom. She then flew back to France on Friday night, arriving early Saturday morning, to be on the ground for the official state visit.

She spent Saturday at an event with French first lady Brigitte Macron and then attended the state dinner with the president. She returned to the United States with the president on Air Force One on Sunday.

Despite the extensive travel, the Jill Biden appeared energetic while on the ground in France. When she and Brigitte Macron toured an art exhibit at the Foundation Louis Vuitton on Saturday, she asked several questions. She and Macron chatted about the art, and, at one point, held hands and giggled. 

For the state dinner, she wore a custom navy blue velvet Schiaparelli gown with a billowing scarf tied around her waist that draped down behind her like a train.

But the first lady faced questions about her extensive travel. 

'The White House should be more transparent about these costs so taxpayers aren't taken for a ride,' Demian Brady, the Vice President of Research for the National Taxpayers Union Foundation told DailyMail.com.

'While I appreciate that the First Lady wants to support her son during this difficult trial, travel to the trial should be a personal, not a taxpayer expense,' said David Williams, president of the Taxpayers Protection Alliance.

Jill Biden spent most of last week in the Wilmington federal courthouse, including her birthday on Monday and on Friday, when her eldest granddaughter Naomi Biden testified on her father Hunter's behalf. 

The Bidens have emphasized their faith in Hunter and are staying close as he fights charges he lied on a federal form when he purchased a gun in 2018.

If he is found guilty of lying about his drug use on a federal form when he purchased a Colt Cobra revolver, he could face up to 25 years in prison.

Two of the counts carry a maximum of 10 years in prison while the remaining has a maximum of five.

Each also has a maximum fine of $250,000.

As it would be his first offense, it is unclear whether he would serve any jail time.

On Sunday, instead of returning to the White House, the Bidens flew the 3,600 miles from Paris to Wilmington, Del., to be there on Monday, when Hunter Biden could take the stand.

Jill Biden was in the courtroom, as was Hunter's sister Ashley and his aunt Valerie Biden Owens. 

'She's his mother, and he's on trial, so of course she wants to be there as much as humanly possible,' said Elizabeth Alexander, communications director for the first lady, told CNN of the first lady.

'It's something that a lot of parents, and maybe mothers especially feel, that when your children need you, it doesn't matter how old they get, they're always your children and you always want to be there to support them,' she added.