Cash-strapped RTE paid €331,000 to send Brendan Murray to this year's Eurovision - even though Ireland failed to qualify.
The spend included the competition entry fee of €84,500 but not RTE labour costs.
The figures were released to the Herald under the Freedom of Information Act.
A delegation of 16 people travelled to Ukraine where Brendan's performance of Dying To Try was not enough to send Ireland through to the final of the contest.
The broadcaster - which reported a deficit of €19.6m in 2016 - splashed out even more when it sent former Westlife star Nicky Byrne to last year's contest in Sweden.
RTE spent €337,000 on his performance in Stockholm - even though the 2fm star waived his performance fee.
The 16-strong delegation that travelled with Brendan to Kiev, the capital of Ukraine, flew economy class and stayed in officially-designated hotels.
Among those who joined the former Hometown star were his tour manager, five backing vocalists, RTE's head of press, a sound engineer, a vocal coach and a photographer.
A "core delegation" travelled to Kiev for two weeks on May 1 for rehearsals that began on May 2. The contest ran from May 9-13.
In defending the cost, an RTE spokesperson said that entering the competition allowed RTE to deliver seven and a half hours of entertainment to Irish viewers.
"This year, an average 273,000 viewers tuned in over the course of the three nights of the contest, representing a 21pc share," she said.
She said that this represented "excellent value for money for RTE and for Irish television licence-fee payers".
"Along with the participation fee, the overall figure includes artist and designer fees, the cost of staging the performance including full dress rehearsals, graphics, props, pyrotechnics, costumes, choreography, postcard filming and song recording," she said.
Brendan was chosen by X Factor judge Louis Walsh to perform in the Eurovision after the music manager was tasked by RTE to select Ireland's entry and the song.
However, there have been calls for the selection process to be changed in the wake of Ireland's failure to qualify for the finals for the fourth year running.
RTE's Eurovision commentator Marty Whelan said it may be time for the National Song contest to come back and things need to be changed next year.
"It's four years in a row and we don't need that again," he said.
"We need to be in the final, so we're just going to see if we can come up with another formula."