While cable TV providers may claim they are competitive in their pricing, they may be adding on fees to cover their costs. Some may include a fee for renting a modem that you may be able to buy elsewhere, which in turn would save you money in the long run.
Also, when you first sign up with a company because they are running a promotion, make sure to look at the fine print. Some companies will have a lower monthly price for the first 6-12 months, and then you will start getting charged their regular fee. So make sure to double-check your bills for any fees you may not have been aware of.