Trump has failed to pay at least 10 of his top staffers - including recently fired campaign chief Paul Manafort 

Republican presidential nominee Donald Trump has run an unusually cheap campaign in part by not paying at least 10 top staffers. 

They include recently departed campaign manager Paul Manafort, California state director Tim Clark, communications director Michael Caputo and a pair of senior aides who left the campaign in June to work for a Trump Super PAC.

The New York real estate magnate and his allies have touted his campaign's frugality, saying it is evidence of his management skills. 

Paul Manafort, Trump's former campaign chief who quit amid the Russian cash scandal, did not draw any salary from election coffers, it has been revealed

California state director Tim Clark (left) and communications director Michael Caputo were also not paid. Caputo has said he was promised a salary, but none materialized

His campaign's spending has totaled $89.5 million so far, about a third of what Democratic rival Hillary Clinton's campaign has spent.

But not compensating top people in a presidential campaign is a departure from campaign finance norms. 

Many of the positions involved might typically come with six-figure annual paychecks in other campaigns.

'It's unprecedented for a presidential campaign to rely so heavily on volunteers for top management positions,' said Paul Ryan, an election lawyer with the campaign finance reform advocacy group Campaign Legal Center.

The Trump campaign said the claims are 'sloppy at best', but declined to elaborate.

One of the 10 who were unpaid, Michael Caputo, told a Buffalo radio station in June after he resigned from the campaign, that he was not volunteering. Rather, he said he just had not gotten paid. 

Caputo confirmed to Reuters on Thursday that the Trump campaign has still not paid his invoices.

Trump has prided himself on the frugality of his campaign, having spent around a third as much as the Clinton camp so far

In another instance, two high-level former Trump campaign advisers, former Chris Christie campaign manager Ken McKay and Manafort lobbying associate Laurance Gay, departed the Trump campaign in June to work for the Trump-backed Super PAC, Rebuilding America Now. 

In June, the Super PAC paid each of them $60,000, the filings show.

Federal campaign law stipulates that people working for campaigns, who may possess strategic knowledge of a campaign or work as a campaign's agents, must wait for 120 days before going to work for a Super PAC, a political spending group that can accept unlimited sums of money from wealthy donors so long as it does not coordinate with a campaign.

Aide Ken McKay left Trump's campaign in June to work for one of his Super PACs without drawing a salary

Through a spokesperson, McKay and Gay said they were volunteering for Trump and did not possess strategic information so the rule did not apply to them. 

Another example of free labor is Rick Gates, who was Manafort's deputy. 

According to two former high-level Trump staffers, Gates functioned as the Trump campaign manager for more than two months, all while not collecting a paycheck.

By contrast, Democratic nominee Hillary Clinton's campaign manager Robby Mook earned roughly $10,000 in July, the same amount as President Barack Obama's campaign manager Jim Messina did in 2012. 

That same year, Republican nominee Mitt Romney's campaign manager, Matt Rhoades, was making nearly $7,000 bi-monthly.

Others who, according to the FEC filings, have not been paid include finance chairman Steven Mnuchin, national political director Rick Wiley and senior adviser Barry Bennett.

None of them were available for comment, nor were Manafort, Gates and Clark.

Many campaigns have volunteers who work as low-level ground troops, knocking on voters' doors and passing out campaign buttons. 

There are instances in other campaigns of senior staff opting not to draw a paycheck. For example, John Podesta, a longtime adviser to Clinton who is now her campaign chairman, considers his role honorary and does not draw a salary.

What is unusual, however, is for a campaign to have such a large group of people in top positions who are unpaid.

After Manafort resigned in August, Trump promoted his senior adviser and top pollster, Kellyanne Conway, to become his new campaign manager.

Before then, Conway ran a Super PAC affiliated with Texas Senator and Republican presidential candidate Ted Cruz. 

For work from June 2015 to June 2016, the Super PAC paid the firm she owns more than $700,000.

She officially joined the Trump campaign July 1. But so far, according to campaign finance reports that detail spending through July 31, Conway has not been paid by the Trump campaign.

She did not respond to a request for comment.