Never will I forget the time a client, the company is out of business now, was approached directly by a radio sales person. The rate per commercial was cheap, cheap, cheap. I was told by the client that it was a great buy. Then I told the client it was even cheaper after the station signed off the air! She said, "really?" That's why she's out of business.
Radio, Television, Cable, Print, Billboards, Internet, they all work. Invest the needed amount of money, make sure what you are advertising is something people want and can afford, and you will see sales as a result.
Two key things here; make sure your product is what people want at a price they are willing to pay, and make sure you invest enough in the advertising to reach your target market(s).