Most safari companies charge around $40 a day for food. This includes a cook, who accompanies you during the trip, sets up the table and makes hot food for dinner and breakfast. Lunch is packed in tiffins. The breakfast is mostly eggs and toast, lunch is usually sandwiches and dinner is something like spaghetti or rice. If you are a backpacker, this turns out to be expensive, especially for a 3-4 days Serengeti - Ngorongoro - Lake Manyara trip.
Fun Alternatives: All camp grounds have common kitchens, used by cooks from all safari companies. You can easily talk to any one of them, and they will give you dinner for $10. Breakfast should cost something similar. You can also pack sandwiches and granola bars for lunch. You can easily save around $20 per day.
Tours to and in Tanzania are incredibly expensive and you are lucky to get a safari for under $80 US with a company. One company I found in Dar Es Salam that provided me with a guide/driver for two full days at a price of $70 US for everything. I was fully impressed with Fun Safaris services and after speaking to other tourists and finding out their price I must say this price was competitive. I loved the safari and despite being $150 or so for a few days it is once in a life time.