According to Forbes, Bert is currently worth $4.2 billion. This makes him the richest Muppet, and the second richest puppeteer after Jim Henson. His net worth comes from a variety of sources, including his ownership of the Muppet Theater, his successful film and television career, and his various endorsements.
Bert's net worth has fluctuated over the years, but has generally been on the rise. In 2006, he was estimated to be worth $2 billion. By 2011, his net worth had grown to $3 billion. In 2014, he was estimated to be worth $4 billion. His current net worth of $4.2 billion makes him the second richest puppeteer in the world, behind only Jim Henson.
Sources:
Forbes - The World's Richest Muppet: Bert Is Worth $4.2 Billion
CelebrityNetWorth - Bert Net Worth