Plumb, who played middle-child Jan Brady, bought the cottage, which sits on Escondido Beach, for $55,300 in 1969. She made a $3.845 million profit in the sale.
Meis Architects -- the same firm that designed the Staples Center -- created plans for what the house could look like with some major upgrades.
"I think that's what helped us to sell it," said William Baker, one of the listing agents for the property.
"It was a fun house to show because you're literally right on the sand and it's one of the most beautiful places in the world," Baker said.