One woman complained of paying 10 times the face value of tickets through a reseller.
Helloworld executive general manager Simon McKearney said the fares were the cheapest since American Airlines launched into the New Zealand market just under a year ago.
"We had $699 to the USA and one year on we have collaborated with Air New Zealand for $699 to their US ports," he said.
"They're definitely the cheapest they have been."
He said Air New Zealand was "telling the big boys that they too can play in that space".
There were no restrictions on the accommodation booked through helloworld and can include a cruise or guided coach tour.
The US fares are from Auckland, Wellington and Christchurch.
Fares on Air New Zealand's Auckland to Invercargill route during May, with a bag, are just under $500.
International airfares have been dropping because of intense competition between a growing number of airlines serving New Zealand.
Last week STA Travel advertised Auckland to London return flights for less than $1000 via Cairns and Manila for $979 return for travel during September, October and November.