TV3's The Nation estimated that the full cost was $7 billion, based on analysis it commissioned by an economist.
Dr Whyte claimed the Conservatives would make up the revenue shortfall by raising alcohol taxes - a policy that deputy leader Christine Rankin appeared to let slip at a candidates' meeting. The Act leader estimated that alcohol excises would have to rise from $2 to $14 to cover the policy, increasing the price of an $18 bottle of wine to $30.
VIDEO: Jamie Whyte in the Herald Hot Seat
Mr Craig dismissed this claim. He said he was interested in the Law Commission's recommendation to investigate an alcohol excise increase of 50 per cent, but this was not to make up for the cost of the party's tax policy.
He said his tax package would be paid for by making government smaller and more cost-effective, such as by making jails pay for themselves through prisoner labour.
Dr Whyte's attack could be an attempt to discredit Ms Rankin, who is running in the Epsom seat that Act candidate David Seymour must win if his party is to be represented again in Parliament. Mr Seymour and Act deputy leader Kenneth Wang spent yesterday walking the streets of the electorate.
VIDEO: Colin Craig in the Herald Hot Seat
New Zealand First leader Winston Peters also put the boot into the Conservatives yesterday in a speech in Invercargill.
He said its stance on another flagship policy, binding referendums, had been shot to pieces after Mr Craig admitted the proposal would require a financial veto clause.
Mr Peters slammed Mr Craig's "personal attacks" on New Zealand First in a pamphlet distributed around the country.
"Mr Craig claims he is taking votes off New Zealand First. None of the New Zealand First voters think that vapour trails are poisoning the people or that the Americans didn't put a man on the moon."
In short, he said, NZ First voters were not wackos.
Meanwhile, Prime Minister John Key spent the day on the campaign trail, starting at Westfield Mall in Glenfield and then moving to Jump Start Kids at Mt Albert, where he mingled with parents and children and then announced the party's Children and Families plan -a mesh of already announced policies.
Read more:
- INTERACTIVE: The major policies - party by party
- FAST FIRE VIDEOS: The leaders on God, flags and cannabis
- POLL INTERACTIVE: Who's strongest with female voters?
- HOW WELL OFF ARE YOU? Use our inequality calculator
- AGEING OF JOHN KEY: Use our interactive to see effect of high office on PM