New Delhi(CNN) India's general election wasn't just the world's biggest.

It was also the most expensive, with political parties, candidates and regulatory bodies spending up to $8.6 billion, according to a new study.

By comparison, the US spent an estimated $6.5 billion in the 2016 presidential and congressional contests, according to Open Secrets, an American non-profit organization.

The Indian estimate, based on research by the Delhi-based Centre for Media Studies (CMS), takes into account spending on both the national and state levels contests this year -- and means that total spending for the 2019 elections that resulted in Indian Prime Minister Narendra Modi winning a second term was nearly twice as much as 2014, when Modi first won national office.

The outcome cemented Modi's position as the most powerful political figure in recent Indian history, with his Hindu nationalist Bharatiya Janata Party (BJP) and its allies securing a two thirds majority in parliament's lower house.

While Prime Minister's personal popularity was seen as a key factor behind the BJP's triumph, the CMS study also shows the party's clear financial advantage, as it built a national campaign centered on the themes of Hindu nationalism and national security.

Indian voters queue at a polling station to cast their vote in Allahabad in Uttar Pradesh state on May 12, 2019, for the sixth phase of India's general election.

The BJP alone is estimated to account for as much as 55% of the total amount spent on elections this year -- or more than $4.5 billion.

Its main national challenger, the principle opposition Congress, led by Rahul Gandhi, only managed about 15% to 20% of the total. Once seen as the natural party of government in India, in the 2019 election, it recorded its second worst performance ever, winning only 52 seats in the 543-strong lower house.

Cashing in

The dizzying costs reflect the scale of the exercise.

More than 600 million people cast their ballots in the 2019 national election, which saw election authorities set up more than a million polling stations.

Some 10 million officials were involved in pulling it all off over seven weeks of staggered voting from April to May.

The total cost for authorities: more than a billion dollars — or roughly double the amount spent in 2014.

A sizable chunk of the total spending, CMS estimates, was in cash, with 10% to 12% of voters in its study reporting direct cash payments.

"Voters were lured with differed offers for their vote," the CMS study said. "Benefits were offered as promises for voting and if party comes to power."

The job of clamping down on such illicit payments fell to India's Election Commission, which seized more than half a billion dollars in cash, gold, liquor and drugs during the course of 11 weeks of active campaigning.