Gareth Morgan expects to spend up to $5 million of his own fortune on his political party - saying he is "donkey deep now and has to keep going".

"I have been surprised [at the cost]. The sad reality of politics is you have to have money to play. And I don't like that," Morgan told the Herald. Morgan has started the Opportunities Party (TOP).

Efforts to bolster campaign war chests are intensifying 100 days out from the election, with the major parties saying the number of new social and media platforms means more will be spent than ever.

From next Friday until September 23, parties can spend up to $1,115,000 on election advertising, plus $26,200 per electorate contested.

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Taxpayer money is also divvied out to parties to spend on television, radio and internet promotions.

Morgan, who made millions through economic forecasting, investment management and investment in his son Sam's Trade Me venture, said a lack of money particularly excluded the young, many of whom can't afford to take time off work to campaign, he said.

Nigel Haworth, president of the New Zealand Labour Party, said it had overhauled its fundraising, with digital and social media at the heart of that change.

"I'm not going to give you the details because this is one of the jewels in our crown, but we have done very, very well indeed. This is something that came through [Barack] Obama, [Bernie] Sanders did it. [Jeremy] Corbyn clearly had tremendous success in the UK with his social media."

Labour recently received $115,000 from retired High Court judge Robert Smellie QC, and Haworth has launched his "President's Club" which has various tiers of donor - bronze, silver, gold and platinum - who give certain amounts each year.

Haworth, who devotes three to four days of his week to fundraising, said most donations averaged $30-$40. He and leader Andrew Little have expressed confidence in the size of the party's election war chest compared to 2014 and 2011.

In 2014 Labour spent half as much as National on the election campaign and was outspent by the Greens for the first time.

National receives more large donations than most parties, but president Peter Goodfellow said the bulk of its fundraising comes from its 30,000 members, with 20 times more donors who give between $5 and $1500 than those who stump up more than $1500.

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Events including lunches and breakfasts are held - "any way which makes it attractive for our donors to meet with politicians" - but the party no longer uses the name Cabinet Club to describe fundraisers where people hear from MPs and ministers.

"It's certainly never been cash-for-access," Goodfellow said. "In New Zealand, in general, you can make an appointment to see the minister or see somebody in the minister's office without having to make any contribution."

Goodfellow said more funds were now needed to advertise on the growing number of media channels. That wasn't just about the youth vote - "even my mother uses Skype".

New Zealand's spending limits limited the influence of money in politics, Goodfellow said, and other parties spent much more per vote than National.

Haworth isn't so comfortable. He said money was increasingly important and Kiwis were noticing "an imbalance in the system".

University of Otago Faculty of Law professor Andrew Geddis said New Zealand was "pretty much in the middle of the road" internationally in terms of controls on fundraising and spending, with no spending limits in Australia and the US.

Spending limits here cover advertising, but not other campaign expenses like opinion polling, travel and staff.

Businessman Colin Craig sunk close to $2m in donations and loans into the Conservatives in 2014, only to see the party get just under 4 per cent of the vote, short of the 5 per cent needed to enter Parliament without an electorate.

Internet mogul Kim Dotcom donated $3.5m to the Internet Party, and Internet Mana received 1.4 per cent. Act topped $750,000 in donations in 2014 and got less than 1 per cent party vote.

Geddis said there wasn't a strong link between spending money and winning in New Zealand, however there were high entry costs for new parties and low levels of state funding for parties (the Greens have called for an inquiry to investigate state-funding for parties).

"Voters know unless a party has a realistic chance of making the quite high 5 per cent threshold, a vote for them is wasted. It's not just money that achieves success, it's been seen as potentially successful."

Largest single declared donations since 2015:

• The Green Party: $283,835 from the estate of Elizabeth Riddoch, August 2016
• National: $150,000 from Inner Mongolia Rider Horse Industry, May 2017
• The Opportunities Party: $150,000 from Gareth Morgan, April 2017
• Act: $100,000 from Alan Gibbs, May 2017
• Labour: $100,000 from Robert Smellie QC, May 2017