SUN holidays can be up to €140 cheaper per person if you fly from Belfast instead of Dublin.
An online travel agency said that sluggish demand in the North means flight prices there are currently cheaper than from Dublin, resulting in significant savings for identical holidays.
Clickandgo.com said that there had been a surge in holidaymakers from the Republic booking holidays from Belfast because of lower prices.
For example, a week's holiday in Majorca departing on May 21 costs €253 per person flying from Belfast compared with €393 if you fly from Dublin.
Both of those holidays involve scheduled flights with Aer Lingus staying in the exact same apartments in Majorca.
The difference is accounted for by the lower flight price. The Belfast flight was priced at €135 per person yesterday compared with €276 for the flight from Dublin.
Flights to other sun destinations such as Faro in Portugal were also slightly cheaper from Belfast, coming in around €20 cheaper per person for travel between May 15 and 22 on Aer Lingus – €147 compared with €168 from Dublin, the Irish Independent found.
Clickandgo.com chief executive Paul Hackett said that the best rates were available to people travelling outside the school holiday months of July and August when fares climbed in both jurisdictions.
However, families with children in secondary school in the Republic could benefit from being able to travel in June, as the North's secondary pupils were still in class then.
The reason for the lower rates from Belfast was that the recession had kicked in there this year but capacity was still at a higher level.
"It simply is a matter of supply and demand that's driving these low prices," said Mr Hackett.
"Holiday sales from the North are weak relative to those from the Republic, so airlines are offering fantastic value to get away through Belfast," he added.
The situation mirrors that in the 1980s, when holidaymakers from the south routinely travelled to Belfast to get better deals.