Buying a whole chicken is the most economical choice. Whole chickens will almost always be cheaper to buy than chicken breast, plus all parts of a chicken are great, not just the breast. Breaking down a chicken is really easy and will save you money in the end. It will also open up a lot of possibilities for where to buy chicken, since most small scale producers can't afford to pay the processing fees of breaking down chickens at the butcher. Here's a great video on how to break down a chicken:
Once a chicken is broken down it will be a lot easier to cook because the pieces will cook more evenly. Also you can cook some pieces now and save some for later in the fridge or freezer, which is a great option for small families that might not eat a whole chicken in one meal.