As a Forbes article points out billionaires are often perceived as driving new Ferrari's and Bentley's, living in Mansions, and flying in private planes. However some multi billionaire who could easily do all of that and more are instead quite frugal. Among the Billionaires they mentioned one cuts their own hair and rides his bicycle 14 miles to work every day.
Among other multi billionaires Warren Buffet worth around $50 Billion still lives in the same house he paid just $31,500 for around 50 years ago.
Jim Walton worth around $21 Billion in 2010. As of the time of the article he was driving a 15 year Dodge Dakota pickup truck. The founder of Ikea (selling affordable furniture) also was driving a 15 year old car - a Volvo and worth $33B when the article was written.
For more Information and frugal billionaires See Forbes.com article by Asher Hawkins 11-14-07 Frugal Billionaires