I floss most nights. I have never had a cavity. My husband flosses now, too. I truly believe that flossing helps reduce our dental bills. We are lucky to have dental insurance which allows us to receive semi annual cleanings, but if we had to have a cavity filled, we would need to pay out of pocket at least some of the costs.
Flossing can reduce the risk of gum disease. Also, researchers have found that flossing reduces the risk of heart disease.
The bottom line is that flossing is worth the 2.5 minutes per night for your health and your bank account.