About 6,450 yuan.

1. 50 people, on average, each person eats two taels of meat or chicken, duck, and fish, one pound of vegetables, and one pound of staple food per day. You need 10 kilograms of pork, chicken, duck, and fish. The wholesale price of pork is 15 yuan per kilogram, which is 150 yuan. If it is chicken, duck, and fish, the wholesale price is up to 8 yuan per kilogram.

2. 50 kilograms of vegetables. According to the wholesale price of 3 yuan per kilogram, it costs 150 yuan.

3. The staple food of rice and white flour costs 2.5 yuan per pound, 50 pounds costs 125 yuan, and a tank of ordinary gas costs 120 yuan for three days, an average of 40 yuan per day. Hiring a cook costs an average of 1* per day. **Expenses are about 180 yuan, so the sum of these times 50 people equals 6,450 yuan. Therefore, the monthly food expenses for 50 people is about 6,450 yuan.