Sky-high speaking fees have become an accepted, if begrudged, staple of the modern post-presidency. Bill Clinton commands upwards of $200,000 for some speeches, and reportedly pulled in a $500,000 donation to his foundation for one. Former actor Ronald Reagan turned his talent into a lucrative third career. Even Gerald Ford defended his right to charge hefty sums for hitting the "mashed potato circuit."

But what if a former president charges $100,000 to speak to a group of veterans wounded in wars he started while in office?

That's exactly what former President George W. Bush did in 2012 – and now, he's coming under fire for it.

Bush charged the Texas-based charity Helping a Hero $100,000 for a 2012 speech at a charity fundraiser for veterans who lost limbs in the Iraq and Afghanistan Wars, ABC News first reported. The former president was also flown in a private jet, at a cost of $20,000 to the charity, which provides specially-adapted homes for handicapped veterans.

Board members told ABC it was a "slap in the face" for wounded veterans.

"For him to be paid to raise money for veterans that were wounded in combat under his orders, I don't think that's right," former Marine Eddie Wright, who lost both his hands in a 2004 rocket attack in Fallujah, Iraq, told ABC.

But the board's chairman told NBC News Bush's appearance helped to raise "significant funds" for the charity. The year that Bush spoke, the charity netted almost $2.5 million; the next year, less than half that amount.

The controversy over Bush's $100,000 speaking fee is the latest in a series of questions over ex-presidents' exorbitant paydays, how they got so high, and whether they are appropriate.

Last month, Politico reported that Bush – who reportedly told author Robert Draper he planned to "replenish the ol' coffers" on the lecture circuit after leaving the White House – makes between $100,000 and $175,000 for every speech he gives. He has given at least 200 speeches since leaving office in 2009, which translates into more than $30 million for the former president in speech fees alone.

Of course, he's not the only one.

Since leaving the White House in 2001, Clinton made a cool $106 million on the lecture circuit, according to a 2013 CNN report.

Reagan faced outrage – and some admiration – for charging $2 million for two, 20-minute speeches in Japan in 1989.

The practice goes back to Gerald Ford, reports Politico, who slowly commanded more and more for his speeches: $10,000, then $20,000, then $40,000, paving the way for his modern counterparts to charge as much as half a million per speech.

“I’m a private citizen now; it’s nobody’s business,” Ford told The New York Times.

How did ex-presidents' fees skyrocket from $10,000 to $100,000 or more?

The Washington Speakers Bureau, founded in 1979, played a major role, writes Fortune.

"The desire among agencies to maximize fees, and the added ability to negotiate that comes with having professional representation, means organizations are more likely to see speaking fees grow," it writes. "Plus, the agency system simply provides more access to influential figures like ex-presidents, meaning more groups are able to get the power elites they want, if they are willing to pay the price."

Organizations like Helping a Hero are willing to pay high fees not to hear Bush's witticisms, but simply to add prestige and publicity to their event and their organization by virtue of snagging a big name speaker.

But while Bush and Clinton have made headlines recently for their sky-high rates, one of the most expensive speeches ever made was by a current presidential hopeful: Donald Trump.

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The billionaire businessman-turned celebrepreneur-turned White House hopeful, who displayed his unusual speaking talents at his own presidential launch ceremony June 16, snagged $1.5 million for a speech at a Learning Annex real estate wealth expo in 2006.

At the time, the organization's president and founder, Bill Zanker told reporters, "He is worth every penny."