I have two Mastiff types around 100lb, two running dogs and a Spaniel X pup. I use about a sack of dry food a month which is £9, approx 60lb tripe/month which costs £24, 60lb hearts/month which costs £30 and the rest is free (rabbit, venison, pigeon, ex egg layers and butchers waste).
So £63 per month and I always put a few quid in the charity pot at the butchers. I have started running me dogs again and before I did I still had 12 rabbits left from the previous season .