it really depends where you live, as the costs will be different. i spend ~ $45 a month. on ~600 rodents
i go through a 50lb bag of food about once a week
and a bale of pine about one a month, the pine is $4.75 a bag after tax
My rats eat a lot more than yours!! I go through about 80lbs of food a week for 150 rats and 2 bags of pine. My food is $13/40lbs bag and the pine is $5/bag. I guess you are dead on with the location and the brand of food and bedding you use.