More than two dozen people have expressed interest in the soon-to-be vacant 1st Congressional District seat, but the field might not be quite so large when filing closes Jan. 28.

Some contenders already are bowing out, including newly elected state Sen. Paul Thurmond, R-Charleston.

Meanwhile, the special election — including the March 19 primary and May 7 special election — could cost taxpayers almost $1 million, and it will be the first major election conducted under the state’s new photo ID law.

Thurmond said Monday he was humbled by the number of people asking him to run but that he could best serve his District 41 constituents by ending speculation that he will seek the seat being vacated soon by Rep. Tim Scott.

Thurmond came closest to Scott in the crowded GOP congressional primary in 2010, and he was among almost two dozen possible Republican candidates to seek the seat again, Charleston County Chair Lin Bennett said.

Thurmond said he hoped his announcement would free up his supporters to rally behind other candidates.

“I also hope that this announcement assures the people of my district that my focus is on serving them not on political opportunity,” he said.

Scott was appointed by Gov. Nikki Haley to serve in the U.S. Senate for the next two years after Sen. Jim DeMint resigned.

Scott will be sworn in Wednesday. Filing for his vacated congressional seat will begin at noon Jan. 18 and conclude at noon Jan. 28, State Election Commission spokesman Chris Whitmire said.

While many Republicans are testing the water about a possible run, only Rep. Wendell Gilliard, D-Charleston, is looking at it, Charleston County Democratic Chair Richard Hricik said.

“I’m testing the waters and crunching the numbers,” he said Monday.

Hricik said he is not sure if the Democrats will have a primary. “I’ve heard rumors about people, but nobody has called me and said, ‘Hey, I’m really interested in running,’ ” he added.

On the GOP side, potential candidates include former Gov. Mark Sanford and his ex-wife, former first lady Jenny Sanford; state Sens. Chip Campsen and Larry Grooms; state Reps. Chip Limehouse, Peter McCoy, Jim Merrill and Andy Patrick; Charleston County Councilman Elliott Summey; Dorchester County Councilman Jay Byars; Charleston City Councilman Mike Seekings; Mount Pleasant Town Councilman Ken Glasson; former state Sen. John Kuhn; former Charleston County School Board member Larry Kabrovsky; former Charleston County Council members Curtis Bostic and Joe McKeown; and Lowcountry businessmen Keith Blandford, Carroll Campbell, Mark Lutz, Bob Menges and Teddy Turner.

Such a potentially crowded field makes three elections — a primary, runoff and special election — more likely, and Whitmire said the State Election Commission did not anticipate the approximately $900,000 cost of these congressional elections in its 2012-13 budget.

He said the commission will approach state budget officials and lawmakers about the shortfall.

“It’s required by law, and the state has to pay for it,” he said. “I don’t know how it gets done, but the state is obligated to conduct a special election.”

Reach Robert Behre at 937-5771.