According to forbes, cuban's net worth is 2.4 billion as of 2010. Some high quality bond would yield him 100million every year, so that's the kind of loss could be easily covered by his interest earnings over the years(wouldn't touch his net worth at all). On the other hand, Les worth under 1 billion so it would be a different story.
Why would any businessman go in with Cuban as a minority owner? Cuban is a great owner, but only if you're a fan. He spends heavily to put a great product on the floor, and in exchange, he gets to be the #1 fan and personality at all the games. Being a minority owner with him means you are losing money and not getting the spotlight. No wonder Perot feels like a fool: He is one.
