Advertising on cable TV has become pricier than doing so on terrestrial networks for the first time, industry sources said Monday.

A 15-second spot during breaks for tvN reality shows "Three Meals a Day" and "Youth Over Flowers" now fetches 25 million won ($21,000), according to sources in the advertising industry.

That's 65 percent more expensive than KBS 2TV's "All about My Mom," the priciest show on a terrestrial network.

"Reply 1988," a popular tvN soap opera that concluded on Jan.

16, charged 22.5 million won for a 15-second slot during breaks.

The nostalgia-inducing series set in the 1980s broke the cable viewership record with 19.6 percent.

The latest tvN series "Cheese in the Trap" is also more expensive than comparable shows on SBS and MBC, according to the sources.

Advertising for the web cartoon-based soap opera goes for 15 million won, which is at least 1 million won more expensive than SBS' "Six Flying Dragons" and MBC's "My Daughter, Keum Sa-wol" and "Glamorous Temptation."

Popular variety shows on terrestrial networks like "Infinite Challenge" and "Running Man" also came up short at around 12 million won, which is less than half the advertising costs for "Three Meals a Day" and "Youth Over Flowers."

Even if advertisers buy a package plan worth 300 million won for "Three Meals a Day," their ads would be shown around once a month, one of the sources said.

A package plan offers discounts on popular programs if purchased with less popular ones. (Yonhap)