French police stopped the man and his wife for a routine traffic check two years ago and found 112 Roman coins in the car.
His wife was fined €3,500 for complicity.
Between 2009 and 2012, the man made dozens of trips to archaeological digs in the region just east of Paris.
During his trial, he said he thought he was acting within the law.
"I looked around on the ground. The objects were there. All I had to do was pick them up," he said.
When police searched his house, they found a veritable museum of objects, ranging from ancient coins and pottery pieces to rings and necklaces.
The court convicted the man, who has not been named, of conducting archaeological digs without permission, selling the proceeds, and illegal possession of archaeological objects.
His ill-gotten gains were ordered returned to the state.
His lawyer, Denis Tailly-Eschenlohr, said the fine was "extremely heavy and totally disproportionate", adding that his client would lodge an appeal.