It all depends on the quality of food you fed them. The less expensive food will cost less up front, but it will usually take more of it to properly feed them. Better quality food is more expensive up front, but they eat a whole lot less of it.My St. Eats about 8 cups of food a day. I have 5 dogs though, so I couldn't say exactly how much he costs. Feeding the whole brood runs me around $100 a month.
I feed my saint high quality food and it costs me about NZD 100 a month.
My girlfriend's brother's girlfriend has one of dem dogs and I'm guessin it cost dem a hole lot to feed that dog.